8.x
Log into the UI as an administrative user.
For 8.17 and below:
Navigate to Troubleshoot > Alerts > All Alerts
For 8.18 and above:
Navigate to Operations > Alerts > All Alerts.
Select the desired Fault Alert and click Actions > Cancel Alert.
Click Yes to confirm and then click OK.
Note: If the alert re-triggers, then the fault alarm is still active on the source.