unity engine How to make a unity mobile game mod

[NPCACES]

I have a mobile game whose server has been shut down. There are some unused models and textures in the game.After I use assetstudio to unpack a single data of the game, I can get two files with the same name and different suffixes named cab-xxxxx.One file has no suffix, and the suffix of the other file is ress.I found that the textures used in this game are taken from ress files.So I want to modify the texture in the ress file, but I don’t know how to modify it.Does anyone know how to modify the ress file?