How big is the tree and how much effort to release? If the tree is big and can potentially put out loads of fruit why not do a bit now to at least give more sunlight and prevent going into decline. Might be another close apple that you just haven't spotted yet or you get motivated to plant one near it.
Have a couple of cases where years after owning my property finally "discover" multiple wild fruit trees. First event was logging and opened up the canopy. After that a dozen trees blossomed for I expect the first time with more direct sun.
The best example was discovering a "hidden" 50 ft pear! And I mean all of 50 ft tall. It was smack dab in the middle of a trio of full sized elms that croaked due to another round of dutch elm disease. Walking up my hill trail one spring and I look up and can see a bunch of white on a tree. Check it out and it's blossoms everywhere. No doubt have walked that part of the trail hundreds of times and never saw it bloom before. BTW, that tree later got released even more so the dying elm did not crash into the pear. Swear not another pear within a 1/4 mile but that thing is loaded every yr now. Sometimes you just get lucky