You need to activate the Developer Options and USB Debugging for the purpose. Follow the below mention steps and you would be good to go:
1.Slide into you Settings > About > Kernel Version.
2.Tap on it Multiple Times and this will grant you the position of a Developer.
3.Go into Settings > About Phone > Developer Options and tap on USB Debugging
4.Now all you have to do is turn ON the Fastboot mode and use the Bootloader.
5.Install recovery for Flashing and find a supporting Custom ROM.
原文：https://www.cnblogs.com/RogerLu/p/14709461.html