How to REMOVE TWRP and ROOT ZTE ZMAX

As someone that once worked in a phone repair shop, it's very disappointing when you can't fix your own device( can't find the part). My aux port doesnt work anymore, and Im starting to see dead pixels on my lcd so I'm going to send in my phone for warranty repair. I can't send in my phone if it has TWRP, I would of asked in the "ZTE ZMAX" section, but XDA doesn't let me post in that section. Any help on this matter will be greatly appreciated.

I was just going to go back to stock, but then I have the matter of TWRP..