You might have Do Not Disturb turned on. If not, then you could restart your phone or update your Clock app in the Galaxy Store. If none of these work and you can, simply clear the cache by going to Settings, scrolling down, and clicking on Apps. Find the Clock app, then click on Storage and clear the cache and data. This will delete your saved alarms in the app, but if it still doesn't work, then it might be a hardware issue.
