Sorry to hear about the pain issue. I don't have the qualifications to diagnose you, and obviously I couldn't diagnose you over the internet even if I did. But a couple of years ago I did rehab an issue of my own that I'm pretty sure was an achilles tendinopathy. I also managed to rehab something I initially thought was an elbow tendinopathy thing, but because it went away fairly fast, I now think it probably wasn't tendinopathy.

Even if your issue isn't tendinopathy, I can tell you how I rehabbed mine. It's how physical therapists on top of their game approach those issues these days. And even if yours isn't tendinopathy, it's not like you'll hurt yourself trying it. The hysterical, catastrophising attitude towards pain that is regrettably common is something we as a society really need to ditch. For all pains there are red flag symptoms that warrant a visit to the doctor. These are things that hint that there could be something that requires a medical intervention. With elbow pain, those things are almost exclusively limited to things that hint at a fracture or infection. Function loss, deformity, swelling, redness or bruising that won't go away, started after an accident, stuff like that. Also if the pain is simply unrelenting, you obviously need help. However, pains with red flag symptoms make up a small minority of all pains and aches. A lot of pains and aches, and certainly most gym-related pains and aches, are not those things. Pain doesn't imply there's something seriously wrong with you, and experiencing pain doesn't mean you caused "further damage". It's ideas like those that make some more fearful people engage in fear-avoidance behavior, which tends to lead to worse outcomes. The narratives we internalize about pain matter for outcomes.

When it comes to tendinopathy, the key issue is that the tendon's tolerance to loading has become worse. I won't speculate on why my achilles tendon had become that way, because it's not helpful and I just couldn't know. But I needed to improve it's tolerance to loading. So how does one do that? Well, by loading it. But how do you load it if it's sensitive to loading? That's where the principles of heavy slow resistance training come into play. Instead of trying to calf raise as much as I could, I lowered tempo down to 3-0-3 (3 seconds up, no pause at the top, 3 seconds down). This limited how much weight I could use by a lot, but gave the tendon a lot of time under tension and allowed me to load it. At first I was a little cautious, cause in truth the exercise still hurt, but after a couple of sessions I figured that the pain wasn't really that bad and it usually subsided quite shortly after training. (When rehabbing these stubborn pains, the rule of thumb they give you is that the pain shouldn't leave you debilitated for the rest of the day and it should return to baseline within 24 hours. If you overdo it, no biggie, just tone it down next time to try and stay roughly within those guidelines.)

The specifics of how to set up a heavy slow resistance training protocol are not set in stone. Ideally, they'd be tailored to your person and symptoms. However, this is what I did with my achilles tendinopathy. I picked two exercises that target the tendon, seated calf raise done one leg at a time in a calf raise machine, and standing calf raise in the smith machine done bilaterally. One was unilateral to prevent me from favoring the good leg, and one was bilateral to allow heavier loading. I did them three times a week. Sets and reps were as follows.

Week 1: 4x15
Weeks 2-3: 4x12
Weeks 4-5: 4x10
Weeks 6-8: 4x8
Weeks 9-12: 4x6

The load was as much as possible, but keep in mind the 3-0-3 tempo severely limited the absolute load I could use. In the last rep I was still supposed to barely be able to keep the weight moving at a consistent speed through all of the range of motion, 3 seconds up and 3 seconds down.

This may not have even been ideal for me. It's just the scheme I found in a source I deemed reliable and ran with it. And it definitely helped a lot. I wouldn't say the symptoms had 100% vanished at the end, but they were a whole lot better. I got back to what I really wanted to do, squat, and didn't really have issues with it. Of course I didn't just jump right back to the weights I was squatting before. I started a little lower, but eventually got right back to normal training. I occasionally had some sensation in my achilles even after that, but I wouldn't call it pain. I guess I'd describe it as a sense of pressure. And that faded with time, too. All in all, worked out really well for a fairly stubborn issue.

Ultimately, how you end up tackling this issue is up to you. What I would do first of all is see if there are any red flag symptoms (from your description, it sounds like the answer is no, but still). Then I'd figure if it hurts during extension against load (for example overhead tricep extensions) or during flexion against load (bicep curl). Then I'd pick two exercises, one unilateral and one bilateral to target specifically the direction that hurts. And then I'd do that three times a week with probably the sets and reps scheme above, or something else if need be. If that was manageable and didn't leave me debilitated for the rest of the day and my symptoms returned to baseline within 24 hours, then I'd stick with the plan. If it was too much, I'd lower weight.

One other thing to keep in mind is that a lot of time our pains and aches end up not being quite as stubborn as we initially feared. Very often when something hurts we can just take weight off the bar until it doesn't hurt and take it from there. Many pains and aches I've had have gone away that way. For certain personalities it's very hard to take weight off the bar, but it's totally okay to do it when you need to, and very often it ends up being all you need to do. Hell, a lot of pains and aches go away by doing that in a matter of a couple of weeks. The heavy slow resistance methods is intended for tendinopathy issues, which are stubborn issues that require this lengthy approach.

Anyway, good luck!