If you are mentoring a student teacher who is completing their initial teacher training (Primary 3 to 7, 5 to 11 leading to QTS or in a secondary subject) you can register your details via this link here https://ccms.bpnsystems.net/applications/index.php?programme_id=84 and select the 'Mentor Primary & Secondary ITT’ intake.
More information about being a mentor can be read here https://www.bestpracticenet.co.uk/mentor
(Please note if you are mentoring a teacher as part of their ECF induction, the above is not applicable.)