I followed a random guide I found on the internet for amd.

In amd case you can do it from their driver by going to performance tab and cjoosing tuning.

There you will find gpu setting, set them to manual and from there you can start changing fan speed and voltage. Voltage you change by 50mv first time amd if stable by 25. When you come to a point where your game/program crashes you the value before that that didn’t crash the game and that’s it.

As for nvidia I don’t know because I don’t own one and don’t have the money to own one ( they are 1k euro on average here for 4070 and 2.5k for 4090 on average ) only thing I know is that you will need msi afterburner.