How to reuse character rig?

Hey guys! I have a 3D character in my game and I have rigged it using Mixamo auto-rigger. As I realised that my character had a lot of polygons for game. I used the rigged fbx in maya and started trimming up the polygons. And when I re-imported the same character the rig does not work and when I go to the rig tab and select configure. the bone seems to be out of the body for some reason.

Please tell me what I'm doing wrong here. And what would be the correct workflow to export a rigged character from maya? I certainly don't wanna pay $79 dollars again to rig the same character through mixamo.

Thank You.

EDITED : As I got no answers so far I thought I should make it more easier for everyone else to understand. I have rigged bones and a character mesh. How do I combine them so it works in unity?