Connections cannot be reactivated, however you add them in again as a new connection with the same email address.
- Select Connections from the left hand side menu
- Select Add a Connection
- Add the connection again but under an alias email. for example: if the account was under "firstname.lastname@example.org" and I've deactivated it, then I could re-add it under "email@example.com". this will resend the connection email to them and it will deliver to their same email address.
- On their end they just need to accept the connection invitation from their email