How do i change the battery on a timex tide and temp watch?

Sometimes you can't do it yourself. It takes a special tool that only a jeweler has. Turn over the back and if it has little notches that takes a special tool. If it is flat you maybe able to pry it off. There should be a little indentation along the edge. Take a small jewelry screwdriver and pry the back off on that indention. If that doesn't come off right away I would take it to a jeweler before you ruin the watch. Some watches aren't worth getting a battery. Just get a new watch.