Go to the Calendar application, open the entry you are deleting and select Options > Delete > Entry.
To delete all the entries before a selected day, select Options > Delete > Before date > Enter the date. You can not delete future entries on your device.
To delete a recurring (repeated) entries, for example birthdays and anniversary entries, open one of the entry on the recurrence and select Options > Delete > All occurences or Delete series.
To delete all remaining entries from the calendar,
- Change the date of the device to the future, for example dd.mm.2022.
- Go to the Calendar and select Options > Delete > Before date > Enter a date in the future (same date as you defined in step 1). This also deletes the recurring events which end before the date you defined in step 1.
- Change the date of the device back to the current date.