Mark Event as Completed
Due to database field limitations it is currently not possible to set a normal event as completed.
In the app, go to Settings > Auto color / Auto icon (which ever you prefer)
Create a new rule "When Notes contains text Completed" use icon / color
In Settings > General > Tools > Add menu item > Set notes
Go back to the menu list and tap set notes
Add "Completed" text in the box and give it a title.
Select an event, then tap the Tools button at the bottomSelect "Set notes" action and select "Completed" text. This should then trigger the auto icon / color rule
However you can try the following workaround: