Purpose of a maintenance alarm is to remind that it is time to inspect the monitoring instruments - check that everything is fine, clean the lenses and things like that. See Maintenance alarms configuration.

If you see that maintenance alarm is active in the alarms window, double click on the alarm line to open Maintenance Periods dialog. There is also View / Maintenance Periods item in the main menu

Click on the corresponding Reset button if the the necessary maintenance was done and the maintenance period can start from the beginning.