Please try these steps and check after each step. If these don't work, let me know. I will provide further troubleshooting steps.
- Run Windows App troubleshooter
Windows Key+X > Click Settings > Click Update & security > Click Troubleshoot > Scroll down to the bottom > Click Windows Store Apps > Click Run the Troubleshooter
- Clear Windows Store Cache
Type cmd in Windows Search box > Right click on Command Prompt > Run As Administrator > Type WSreset.exe and click Enter > Reboot your computer
- Try to reset the app
Windows Key+i > Apps > Scroll down to this App > Click this App > Advanced options > Reset
- Uninstall and Reinstall Alarms and Clock app
A. Uninstall - Windows Key+X > Click Windows Powershell (Admin) > Copy the below and paste into Powershell and Enter
Get-AppxPackage Microsoft.WindowsAlarms | Remove-AppxPackage
B. Reinstall
Windows Key+X > Click Windows Powershell (Admin) > Copy the below command and right click in Powershell to paste > Enter
Get-AppxPackage -allusers Microsoft.WindowsAlarms | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register “$($_.InstallLocation)\AppXManifest.xml”}
(If there is a problem in reinstall, you can always reinstall from MS Store)