Remove the scope and rings from off the bases.
Press the objective lens firmly against a mirror in a bright room, and look at the image. You will see the reticle and a somewhat dimmer reflection of same.
Adjust the windage and elevation until the two coincide. The scope will now be very close to optically centered.
I put a 1" dowel in the rings. turn front ring so dowel is directly over the barrel/muzzle. Add 2nd ring and tighten windage screws accordingly.
Replace the scope on the bases, and adjust the windage screws in the rear base while bore sighting until the windage is correct.
Head back to the range, and start your sight in at 25 yards.
Your first shot will definitely be on the paper, and most likely only need one more to be centered on the target.
Now ready to sight in at longer distance. It usually takes three or four shots to be sighted at whatever height above zero you wish at 100, and the another three to confirm the sight-in group.
Shoot to confirm group sizes and trajectory at longer ranges.
Ted