My watch needs a new battery.

There is a tool that you need that adjusts to the three holes or openings in the back of your watch and it just screws off. If you don't have access to the tool, simply take two push pins and CAREFULLY insert them into the openings and unscrew the back cover. Remember that it unscrews counter-clockwise.This will give you access to the battery simply take it out and go to the store to buy a replacement repeat the process to install the cover back on.