/ekx/ 1 switch

Get off custom firmware, hope you managed to do the emunand setup

The next following steps are without customfirmware, meaning you will be able to go online.
Enter RCM
Run tegrarcmgui.exe
Click tools --> Mount and mount eMMC rawNAND Ignore the warning, and if it asks you to install something, do it. after finishing, the green rcm light must turn red, close tegra.

Getting your biskey3
If you followed the above guides you should be having your keys backed up.
Open prod.keys with a text editor, ie: notepad.
look for this line: bis_key_03
coppy all the string after the = sign and copy to another notepad file. It must be a 64 character line.
Divide this line into 2, first 32 characters will be your upper, and last 32 characters your lower.
save and keep this file

Hackdiskmount
https://files.sshnuke.net/HacDiskMount1055.zip
Open using Admin priviledges
File --> open physical drive --> doble click user
A new window will pop out. use the keys you got using the biskey3 and allocate them in the text boxes.
click test and if green, you can proceed to install the driver, I use drive letter A, install and then mount it.
Open your files and navigate to the driver you installed the mount. Open the save folder and look for file 0000000000000034 (pokemon sword) I don't know pokemon shield since I have sword. transfer to desktop/wherever and make a backup file also.
This is the savefile that the system has of the game

>but anon, I cannot pkhex this
Here comes the tricky part.

Hactool.exe
https://github.com/SciresM/hactool/releases
Download to a folder

https://files.catbox.moe/gd1c0q.rar
Download to same folder
Copy your prod.keys file to this folder as well.

Make two folders
>sav
>out

copy one of your save file copies to the sav folder and run extract.bat
that will bring the main archive compatible with pkhex into the out folder
when you are done with pkhex, put main back inside where you found it and run inject.bat
take out the file in sav folder and overwrite the file in the save folder of the mounted system.

UNMOUNT HACKDISKMOUNT, don't unplug your switch without unmounting!
after unmounting, turn it off by pressing the on/off button till the screen goes completely black and turn it back on

If you did everything correctly, the injected save file is up and running.