Hello, try two things:
1. Settings / Applications, three dots up right-Reset preferences.
If this has not worked for you:
2. Hold down the Clock app icon, you will see iboton, click, the three dots on the top right-Uninstall updates. This will restore the app to its initial values. You can always update it to the latest version.
All the best.
"The quieter you become-the more you are able to hear..."
@EmmaBaker: I'm not sure if this will work, but you could try pressing the Side Key to snooze or turn off the alarm if you have a lock screen option in place. Let me know if this helps.