hiii i like cute things. lmk if somethang break or whateva <3
im friendly i swear! feel free to pm me to chat if you'd like :D

decent blender knowledge and lesser unity understanding (more a user than creator) so i might chime in to help.
i wont do ur unity work tho

i only use mega sowwy

[Locate] %appdata% > LocalLow > Vrchat > Vrchat >Cache-WindowsPlayer
[Info] This is your (personally) downloaded cache; worlds and avatars stored inside this folder.
Nothing will be named right just be aware of newest downloaded will be top of the list.

Opening the model file will display a '_file" file extention, copy+paste this to a new location you can easily get to and rename it to anything but make sure you end with '.vrca'
This is now changed into a .vrca readable file you can open with SARS/ARC.

Load the vrca file and export with ARC, I will not guide past this point here but wish you the best with recovering a old model/etc.
<3