How to factory reset my 2008 Macbook?

Those models generally shipped with system install-restore DVDs.

That's the first item to have/save/keep & use to reset/restore OS X.

And that would be 'grey-color' label with Apple part number, for

one specific series build model 2008 MacBook. (There was more

than one build model in that year, btw.)

Good luck & happy trails!🌤🌻