TCR
Your scope should have an adjustment for Parallax, an adjustment for magnification and an adjustment for reticle focus. The Parallax/focus adjustment is the one with distances marked on it, a ring at the objective end of the scope or a dial on the side of the scope. Magnification is obvious.
Reticle focus is the rearmost adjustment on the eyepiece and secured with a locking ring. It is adjusted by holding the rifle up at a light sky and QUICKLY look through the scope at the reticle. (DO NOT continue looking as your eye will automatically compensate for the reticle focus) Do this quickly and for very short periods of time, adjusting the eyepiece until the reticle is focused when you look quickly Then lock it in place with the lock ring.
Then mount your scoped rifle on a good rest. Find a verticle post or pole or any clear verticle item at 100 yards. Align your scopes verticle crosshairs with the verticle post. Then carefully, without touching or moving the rifle move your eye back & forth behind the eyepiece, watching the crosshairs on the post.
When Parallax is dialed out, the crosshairs will not move as you move your eye back & forth. You can adjust the Parallax ring or dial until the reticle does not move as you move. Then at that distance, Parallax is adjusted correctly. Parallax settings WILL be different at longer or shorter ranges.
I usually use a little dot of white out to mark the correct position of the focus / parallax ring or dial.
NOTE! you may not be at the marked distance when you have dialed out the parallax. Only two of my scopes actually coincide with distance and parallax free settings.