Program admin can invite a mentor to volunteer for a mentorship program by adding her as a mentor. When admin adds a mentor, the mentor receives an email notification from LF Engineering letting her know that she's been added and asking her to create a mentor profile if she doesn't have one.
If a mentor already has a profile on LFX Mentorship there is no action required, unless she wants to remove herself from the program. Below is a screenshot of the email that mentor receives after being added by the program admin.
A mentor can remove herself from a program by navigating to her profile and selecting Remove From Program CTA next to the program name she wants to be removed from.