If you're having trouble changing the day or date on your watch, it most likely means that the wheel has become stuck. Here are a few tips to try if your watch's day or date is stuck:
1) Try gently rotating the watch's bezel in both directions. This can sometimes free up the wheel and allow it to move smoothly.
2) If that doesn't work, remove the battery (if possible) and re-install it. This can often free up the wheel and allow it to work properly.
3) If all of these methods fail, you may need to take your watch to a repair or jeweler for service.