Walk slowly over the entire engineered wood floor surface in side-by-side rows to identify all of the squeaky locations. When you step on a board that squeaks, mark it by placing a piece of masking tape on the location.
Insert a putty knife into the floor boards in one of the squeak locations, working it carefully down as far as possible to the concrete subfloor.
Twist the handle of the putty knife gently to the side until you achieve approximately a 1/8-inch gap between the boards. Use care not to twist it too far, otherwise the engineered boards may pop out of the floor.
Insert the tip of a bottle of carpenter’s glue on top of the crack and squeeze the bottle gently to push glue down into the subfloor.
Hold the putty knife in place for 20 to 30 seconds to allow the glue to seep in and then remove the knife from between the floor boards.
Saturate a rag or sponge with water and then wring it out until it no longer drips. Wipe the surface of the floor to remove the excess glue that seeps out.
Place a heavy object, such as a chair, on top of the area to hold the boards down for 24 hours until the glue dries completely.