Step for step guide:

Download AMD Blockchain driver or adrenalin driver (you have to set to compute mode)

Mod your driver with
https://www.monitortests.com/forum/Thread-AMD-ATI-Pixel-Clock-Patcher
so it accepts modded bios

Download bios from your card with atiflash 2.77

Modify it with https://github.com/jaschaknack/PolarisBiosEditor
Use one click timings if in doubt

Reflash your card with atiflash and the modded bios

Reboot

Enjoy 28-32 MH/s