A: Hello kasra1637,

TidyCal has two email reminders that will go out either automatically or at 24 hours before the meeting and 1 hour before the meeting, OR you may edit those email reminders in the edit mode of each of your booking types.
You may modify the content of those reminders and the timing they will go out by editing one template in each booking type you have.
Please keep in mind those two email reminders are exactly the same (so you edit one template), and all you need to do once the reminder email is set is to adjust the times those reminders will go out to your clients.

With kind regards!