At the end of your objective scope is a ring. It’s the last 1/4” or 1/2” of the end of the outer section of the scope (just past the gold ring, the gold ring is also it’s own piece). Unscrew that using a strap wrench or something non-marring. Do this with the scope at max magnification.
You will need to be careful not to unscrew the lens carrier while you are doing this. If the lens carrier is coming out with the ring, then you will need to use the two slots that you can see inside the outer housing of the objective lens. You can probably find a piece of metal that will fit just inside the objective and slide into those slots to act as counter rotation.
Once that ring is off, you should then have the lens carrier exposed. It should smoothly screw in or out, kind of like the ocular focus at the other end. Do not take this piece out.
You can gently move this in and out to see where you need to be to adjust the parallax where you want it. There is a rubber O-ring that seals in the nitrogen, so don’t unscrew the the thing far, just make small adjustments while checking the scope to see how your parallax is.
Once done screw the end ring back on.
I included pictures of an old beat up and painted Leupold 1.5-4 that I just took apart for you (it had failed and had moisture in it). You can see the lens carrier with the O-Ring, I circled it in red for you and reminded you not to take it out
. It will very likely try and unscrew when you begin unscrewing the outer ring, so watch for those notches to start turning and if they do, place a flat piece of metal in those notches to keep it from turning while you continue to unscrew the outer ring.