Need quick and simple help. :D:D

Hello my friends,

I need your help, right now I’m trying to build my own head as a helmet I or someone else could wear.
I have a nearly finished 3D-Model in an obj. file.
My Problem now is that the texture is kinda flawed, the back of my head is not completely ‘painted’.
I would celebrate, if someone could help me out here. For someone who knows Blender it would probably only take a minute…

I’m counting on you. :D:D