Cut a small 'X' in the center of the bubble with the utility knife. This allows trapped air to escape from beneath the vinyl.
Roll over the space with a rented floor roller to flatten it. Alternatively, place a towel and warm iron on the spot for a few minutes to soften the adhesive, so that it can form a more secure bond between the vinyl and subflooring.
Place a heavy book or full paint can on the area to maintain contact between the adhesive and the vinyl.
Check the repair in about an hour. If the vinyl has not completely flattened, carefully widen the hole slightly with the utility knife and place a small bead of vinyl adhesive into the hole. Place a piece of wax paper on the area and then weigh it down as described in Step 3. The wax paper prevents the book or weights from sticking to the vinyl.