Tag Heuer is a high end watch with an expensive movement. If the watch is quartz, you can open the watch to replace the battery, if you are familiar with working on watches. If the watch has an automatic movement, you must be very careful when opening the watch, because the delicate movement can be damaged.
Look at the back of the watch. You will see grooves around the edge of the case. Set your watch case wrench to match the size of the case and fit into the grooves. This wrench is easy to use and is made for use on watch brands such as Tag Heuer.
Twist the wrench to open the case back after the wrench is secured in the grooves.
Remove the rubber gasket from around the edge of the inside of the case. Keep this handy for when you close the case. If the gasket is replaced incorrectly, it will ruin the waterproofing of the case.