You have to engage play mode for the head to come up and engage, when that hole aligns with one of the spring loaded play back head alignment screws. In most cases that screw will have spring under it for back and forth movement of the head, when the other side of the head assembly is fixed.
So in play mode, that hole aligns to the head alignment screw. Then one can easily put a screw driver straight to the screw head.
In stop position that screw and hole won't align.
I believe that is the hole you are referring to.