1st open back case of the unit
2nd unplug the battery
3rd open UT
4th click the vivo tab search vivo y31 the click the factory reset
5 get the twizzer for testpoint
6 insert cable from pc to unit
7 wait until to finish or done the process
8 plug the battery and open the unit and set up it then it's done
pahiram muna po ako ng isang pict para s tp for ref. lng nd kz kita ung sa akin credit to owner nlng po s isang pict. salamat...
sana maka tulong