Help changing the player's arm mesh

I want to change the player’s arm mesh but keep the shirts texture on like the original arm

If I try to add a mesh or a character mesh to the player’s arm, it glitches out the texture

I have tried to use a character mesh and used the player’s shirt texture ID, but it still doesn’t work.
If anybody knows how to do this, please tell me!

I’ve been stuck with this too. Mainly after deleting the humanoid, how do you possibly map the shirt and pants?

Best solution I have is to just map all the UVs yourself in the 3D modelling program.