Can someone please give me a step by step guide on how to root developer rom 6.7.7 please. If i use miunlock it keep giving An error at the first step and the recovery keeps rejecting new roms
You're confusing. The root permissions are one thing, the bootloader unlocking is quite another.
Miunlock is a software for unlocking the bootloader.
Have you requested the bootloader unlock to xiaomi?
I think you have a problem with xiaomi drivers.
Download Mi Flash tool or Mi Phone to correctly install the drivers.
If this doesn't work, try with another PC.