getting rid of squeaks
Best way I know is from underneath.
Could be a few different methods needed. You need a helper walking around on floor to make it squeak, while you locate it underneath.
You often can see the movement in the boards, determine if you need a few screws to tighten it up, 1 1/4" should be fine.
Sometimes a wood shim with some liquid nails on it driven between joist and diagonal sub floor.
Or a longer screw toe nailed threw joist into subfloor. All the while with helper working with you to see what affect you had. Sometimes you may need to add a block in between joist glued and screwed. Is several ways and need to get creative and try a few.
You can just screw it from the top, try a screw here and another there, end up looking like you took a shotgun to it and totally destroy the floor from ever refinishing in future.
If it was easy, we would not call it work!