Simply identify the squeaking board, then get a friend to put pressure on the floorboard so you can identify where raised boards are flexing against the floor joists.
Mark where the boards are raised from the floor joists with chalk.
Spread Selleys Aquadhere Durabond on a thin wooden wedge and tap it between the floor joist and the floorboards with a hammer. Choose a wedge that’s thin enough so it just fills the gap but doesn’t raise the floorboards.
If you have access from above the boards..
Start by moving any furniture and carpets, then follow the instructions above to locate the squeaky board.
Using a stud finder, locate where the floorboards cross the floor joists.
Drill a pilot hole for a screw through the floorboard and into the joist. Enlarge the hole at the top with a bit that’s as large as the diameter of the screw head, so you can sink the head of the screw just below the surface of the floorboard.
Drill a similar hole into floor joists wherever you find a raised board that squeaks.
Screw flat head screws into the holes while someone stands on the floorboards, making sure the screws hold the floorboards down tightly. Make sure your screws are long enough to go an 2cm into the joist below.