On the Mobile platform:
To delete the triggered alarms, which have already expired, go to: More > Alarms > and tap on any of the triggered alarms. You will a pop-up menu, which allows you to "Delete Alarm" or "Delete all Triggered Alarms".
On the desktop platform:
Go to the icon "Server Side Alerts", which is a ringer bell on the fixed icon menu bar (on the right-hand side of the time frame drop-down menu). From there, if you right-click on any of the triggered alarms you will have the option to delete the alarm or delete all triggered alarms.
Trade Interceptor's server based alarms are part of the Premium Services. For more information please go here.