Hey stufromhalifax,
If you use iCloud as your method for keeping your calendar up-to-date across devices, then the steps below from the following article can help show how to restore calendars and events: Restore your calendars and events on iCloud.com - Apple Support
"If you don’t have shared calendars, go to the next step.
If you do have shared calendars, write down which ones you’re sharing, who you invited to share each one, and whether each participant can view and edit or only view. Also note which calendars other people are sharing with you.
2. On iCloud.com, go to Account Settings, then click Restore Calendars in the Advanced section (or Restore Calendars and Reminders if you’re not using upgraded reminders).
Available versions are listed by the date and time they were archived.
3. To the right of the version you want to restore, click Restore.
There may be more versions than can be displayed. Scroll to see them all.
Note: Wait until iCloud finishes restoring your calendars before you change them. During the restore process, any changes you make aren’t saved.
4. If you had shared calendars, reshare them and ask other people to reinvite you to share their calendars and reminder lists. See Share a calendar on iCloud.com."
If you don't use iCloud for your calendars, another step you can try if you use Time Machine is to restore those as seen here: Restore items backed up with Time Machine on Mac - Apple Support
Take care!