Hello @StacyW2 ,
If a contact was ever unsubscribed then had to be resubscribed (will show resubscribed by X as of Y next to the email address), the ability to edit their email won't be available. This is because that coded contact ID is now locked to that email address, for Compliance reasons. The best option would be to create a brand new contact for this email address, and simply fill in all the respective contact fields and put into the applicable lists.
If you don't believe this contact was ever unsubbed / resubbed at any point, feel free to reply directly to the automated @ mention email with the contact's current email address, and we'll investigate further.