Have a closer look at the front dovetailed scope mount. See if there's a witness mark, a line that has been stamped into the steel that moves when drifted - to line it up with a second fixed stamped line. They don't necessarily have to be exactly even, but as you adjust, you'll have a point of reference. You might also consider using a 0.001" dial caliper to keep some track of how much adjustment you have done and the result on the POI. That way you can best judge how much more is needed. Be careful doing any drift adjustment you don't mar the metal. I use a small piece of flat, hard wood to sit on what I want to hammer and then use a soft faced hammer on that. The rifle will need to be held steady. A leather sand-bag or two at the range will usually do the job and you might pack things with a silicon cloth or similar. Take your time to do this adjusting carefully.

Plan B is to look for those 2 opposing rear-mount screws and use 1/4 turns as instructed. If at first it doesn't work, use some penetrating oil as the mount may be seized. Use close fitting screw drivers. If there's no witness mark there, use the side of the mount as a guide. Also make sure any oil used can't find it's way anywhere near the optics.

Some bullets will take on a bit more or less lateral movement and you could try to find a bullet that will land exactly where the POA is. There's a good chance it'll work. However, unless you find a suitable bullet fairly quickly, I'd choose what I considered the best bullet for the job and then make small adjustments to the front or rear mount to accommodate it. A change of powder might work, but a different bullet is more likely to move POI. Only one way to find out for sure!