[HELP] How to edit 3D signs

Hey there guys!

So im having some issues with editing some 3D signs, for example in the Mission Row PD, there is a sign behind the lobby “Los Santos Police Department” which is 3D and id like to edit this, the same with some other 3D signs.

How do i do this?

I have tried adding them into zmodeler3, it says the files and textures have loaded in but it doesn’t show anything? any help would be greatly appreciated!

Thanks in advance!