Help a noob alter a cloak mesh

Hello.

In Skyrim and Fallout 4, we have a mod called Outfit Studio that allows one to change the mesh of clothing to hide clipping, by painting the desired area making it more convex or concave, depending on the situation.

I don’t think there is such a tool for NWN, but I would like to do something similar to the Hooded Cloak, because when you lay a trap or put something on the floor, his right arm goes through the cloak. Although just a small thing, I like this cloak very much and it bothers me a little.

I don’t have 3d model software experience, only a little bit of Photoshop, but I think it must not be very difficult. I think I already got the file I need, “pmh0_cloak_003.mdl”, for human male. Can someone point me a tutorial, or tell me how to do it, which software to use? I hear people talk about Gmax, but I’ve never used it.

Thank you very much.