All email templates are located in Edit form - Settings - Email Templates. The email templates for your mentoring form are located towards the bottom section of the email templates section.
Please note that these emails will be instrumental in informing both the Client and the Mentor of the process and the steps they need to take i.e. in the Mentor assigned - Mentor notification (free & paid) there should be a message saying they have a certain amount of days to contact the client. Or in Mentor assigned -Applicant(Client) Notification there is a message to the Client "If you do not hear from the mentor in the next 7 days..."