Shoot it of a rest just like you would a rifle. A crossbow at 30 yards off a rest should be very, very consistent. It shouldn't take you more than 4 or 5 shots to zero it perfectly.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.