ZModeler forum

Hello guys I have been scouring the internet trying to find a good tutorial on how to convert a 3d model for example an obj model of a Gun into a ydr of a gun and use it ingame but I have no idea how to go about doing this, all help is appreciated

import original gun model,
import your .obj file. replace the geometry in original model's hierarchy with your loaded model. You can can use "Display\Local Axes\Copy" tool first to copy axes position from original part onto modded part.
assign original material onto your modded geometry.

export and test in game.

then adjust original material - put proper texture, the one that matches your .obj file. Put this texture into .ytd file too. export and test in game.

the best way is to practice with modding of original guns by adding some parts/geometry (with modify/attach tool) as the very first modding steps.

Sorry I do not quite understand, especially text tutorials do you know any video tutorials on how to do this?

Nope.
However, you can search on youtube, I guess there are some tutorials on weapons modding. I personally never made any of a kind.