Need help with undervolting my cards

[Kryptowolf512]

Hi guys,
im never tried undervolting and im mining like 2-3 months.
My cards:
EVGA GTX 1080 Ti Hybrid
Zotac GTX 1070 Amp Edition
XFX Radeon Vega 56

The electricity is really expensive here in my country like almost 0,30$ and i heard undervolting can bring wonders to my profitability.
Can you guys help me?
Regards