You can safely open a Tag Heuer watch through careful removal of the case back without any new damage to the closure. Seals can be inspected and lubricated or replaced once the watch is open. A gently opened timepiece retains its watertight seal once closed.
Search the back of the Tag Heuer watch for small screw heads along the outer rim of the case back. Twist the screws out gently with a tiny Phillips screwdriver. Keep the screws together in a small container for use during reassembly.
Adjust the three prongs of the watch case wrench until they fit snugly around the outer rim of the case back. Tighten the knobs on the top of the tool to lock the prongs in position. Grip the sides of the case back with all three prongs and twist counterclockwise.
Lift the case back up and off the Tag Heuer watch case. Set it aside on a smooth, clean surface. Peel the case back seal off the inner rim of the case back with a pair of tweezers if it sticks on.