@Rainstorm I opened it just to see and you can actually open it in unity since it's a fbx, you have the bones but not the physbones made or any shaders added, I took the liberty to add them and while I don't know how to put Modular avatar I think you can just put it on the head bone, I also made a second material with liltoon on it so it could look better, maybe you use another shader for your avatar so I would just drag and drop what you like on it µ
I think I exported it correctly (second time i do that tell me if it worked correctly)
password: CatBeanie
Download Link (workupload.com)