I've done this in the past. You'd need to mod the CPU and optionally the board too.
It's not guaranteed that it will work!
Some motherboards support it, others don't.
Basically what you need to do is to join two pins and isolate three pins. You could also join a group pins to set your desired voltage in case your motherboard doesn't let you change that. You will need a very thin wire. One of the filaments from an 80-pin IDE cable is ideal for this.
It is a bit hard and destructive. Today I wouldn't do it on CPUs that I really care about. But if you have a lot of them or you are willing to sacrifice one, it's fun.
The last step, the one that involves isolating the pins is the one that's the most destructive, because you'll either have to destroy the socket or you could avoid much trouble and cut the pins on the CPU and keep the motherboard intact.
Either way as I mentioned, it's not guaranteed to work so keep that in mind.
Refer to this
https://www.overclockers.com/tualatin-in-a-bx-board/
Good luck!