Hi @JohnWayne,
HubSpot makes this a bit harder than it could be. In your case, the fastest way to re subscribe the contact is for them to find an old marketing email and adjust their preferences via the preferences link. Resubscribe contacts to your marketing emails
For these operational emails, HubSpot has a paid add on: How to Use Transactional Emails to Send Relationship-Based Emails in HubSpot
These will also be sent to fully unsubscribed contacts.
Best regards!