Hello everyone
Replace the male01.dff and the male01.txd files in gta3.img.
gta3.img is located in the models folder in the main path of the game and you can open it with software such as TXDWorkshop and perform the replacement operation.
Of course, the best way is to use skin loader mods such as Skin Selector, so in this alternative way the original files won't got damaged.

The model designer was Jared64, you can visit his page

 https://sketchfab.com/Jared64