kb routines is a personal app, run for its owner's own use.
What it accesses: the Google calendars you choose, to create, update and remove the events of your routines.
Where your data goes: it stays on the computer that runs kb, and goes nowhere except back to Google Calendar. It is not sold or shared.
Google user data: kb routines' use of information received from Google APIs adheres to the Google API Services User Data Policy, including the Limited Use requirements.
Removing access: remove the account in kb, or revoke access at myaccount.google.com/permissions.