Most modern diving watches include a unidirectional bezel that allows timing a dive. A bezel protects the watch crystal while also keeping any blunt force from impacting the side of the watch case. A bezel can become damaged. But with the right tools, it can be removed and replaced.
Lay your watch face up on a soft cloth to avoid scratching the band or back of the watch case.
Tear off a few strips of masking tape, and then slide them underneath the bezel to prevent scratching the case under the bezel. You can also tape the surrounding lug area to prevent scratches.
Slide a pocket knife blade under the bezel on top of the masking-taped sections. Rotate the knife gently downward to pop off the bezel.
Remove the bezel carefully--if the watch has a movable bezel (which most diving watches will), be mindful of the small spring at the 12 o'clock position. This is what causes your bezel to click when turned, and it must stay in place.
To replace the bezel, place it on top of the watch in its original position, and push equally on both sides of the bezel until it clicks in place. Make sure it rotates correctly before wearing the watch.