I would recommend you go through the User Manual and see how you can use the
Completed events expiry date, the
Expiry period type and setting up the
Completed events expiry date
Defines the number of days for which you can edit a completed event. This means that when an event is completed and the specified number of expiry days has passed, the event is locked.
If you set “Completed events expiry days” to 10", an event is locked ten days after the completion date. After this date you can no longer edit the event.
Expiry period type and Expiry days
The expiry days defines for how many days after the end of the previous period, an event can be edited. The period type is defined by the expiry period type. This means that when the specified number of expiry days has passed since the end date of the previous period, the events from that period are locked.
If you set the expiry type to “Monthly” and the expiry days to “10” and the month is October, then you can’t add or edit an event to October after the 10th of November.