There might be a number of places inside Appointment Reminder where you might need to change your email if this has changed.
1. Change your profile email address.
2. Settings > Business Settings. Update the address where invoices are emailed to.
3. Go to Calendar > Edit Calendars > Edit. Check the email address where replies from customers are emailed to. This might need changing.
4. If your connected calendar (such as google calendar) has changed and not connected to a different external account you maybe need to re-authenticate you calendar. Go to Calendar > Add Calendar > Google Calendar (for example) and click Re-Authenticate.