They didn't do that at the store for you? You kinda need another person for it. I had Norm at the Bow Rack do it once for me and ever since then I've just worked off his example by measuring. Ultimately, you want the peep to be at eye-level when the string is at the corner of the mouth at draw. Then straight ahead to the upper sight pin. Did they string-nock it for you? That's the starting point you need first.

What's really important is getting the arrow rest centered off the string. They sell devices and lasers to do this but it can be done with two straight arrows.

Remember, the worst day shooting is still better than the best day working.