How do I fully revoke Tickr's access to my calendar?

Two steps:

1. In Tickr: go to Profile → Calendar section and click Disconnect. Tickr deletes the OAuth tokens from its database.
2. On the Microsoft side: go to https://account.microsoft.com/privacy/app-access, find Tickr in the app list, and click Remove these permissions. This second step is what revokes access at the token level; without it, the refresh token would theoretically remain valid until its next expiry on the Microsoft side.

Tickr entries already imported are not affected.