does this work?

local idleanimids = {5980688357,5980695371}

game.Players.PlayerAdded:Connect(function(plr)
	local char = plr.CharacterAdded:Wait()
	while true do
		char.Humanoid.Health.Changed:connect(function()
			if char.Humanoid.Health <= 50 then
				char.Animate.Idle.Animation1.AnimationId = "rbxassetid://"..idleanimids[1]
			end
		end)
		wait()
	end
end)