Need help flashing root access on zte z831

Hello, I have a phone ZTE MAVEN 2 Model Z831, I try to root, but I should first flash a custom recovery, in order to flash supersu. I already compile my own version of TWRP recovery, but I don’t know yet how to flash the recovery.img file on my phone. Please, can someone help me? I can’t try to flash on fastboot mode bootloader mode don’t work on this phone. so, i need help. Waiting for your answer anyone, Thanks!

I’m afraid this question is pretty off topic for this forum. It is (remotely) possible someone here will help but you would be much better off asking on a more suitable forum, perhaps XDA developers?