Flange not level

I am in the midst of a remodel, hoping to repair damaged floor and install new toilet on existing flange. Plastic flange appears to be in good condition other than the fact that seems to lean slightly toward the wall. (Perhaps the cause of damaged floor!)

I am able to access underneath. How far back do I have to go to go to right this wrong? Sorry no pics.

You're on the right track, the flange must be replaced so that it is level. It also should set on top of the finished floor, not recessed below that level. Since you say the existing flange is plastic, I will assume you have either ABS or PVC plumbing to deal with. You don't need to go too far back to correct the problem. Cut the old pipe off before the closet bend, remove everything from the cut to the bathroom floor, and splice in new parts starting with a coupler. It would be easier on you to not make the final pipe cut for the flange until after the floor is replaced. That way the proper height will be known. The flange is not only glued but also should be screwed through the finished floor and sub floor using #12 Stainless steel or brass screws. I prefer SS because steel is stronger than brass and therefore less likely to break. Cut the sub floor and finished floor so that there is very little space between the pipe and the floors. Come on back if you still have questions, and don't be surprised to find several more suggestions.