If you are familiar with ride the lightning by metallica you will know which part I'm talking about. In the solo there is a harmony bit.

I have a boss GT-8 I have already kind of set it up the harmonist effect but I don't think its absolutely correct. My setting right now is I think 1-Voice, HR1 -5th, key C.

I think either its -5th or +5th and I'm not sure what key it should be in.

If anyone has done this before please message me soon.

Uh, you should learn about keys and figuring them out rather than having someone tell you. Its a very useful skill. That said, I would skip a using a harmonizer and just use a slightly delay so that it doubles the signal.
I know it was too specific this question. Well I will just mess around with the effects for a while.

But if anyone has done this before please post some tips.