Change Completed status of an activity
When you consider that an activity is finished, you can mark it as completed.
Completed is a toggle option, which you activate and deactivate using the same menu option or shortcut key. A tick specifies that the activity is Completed.
Do one of the following:
Right-click the activity and choose Completed.
Mark the checkbox in the Completed column in the Activities section tab.
Open the follow-up and select Completed.
To edit a completed activity, you must first uncheck the Completed status.