When a contact reaches out over phone or email to ask to be unsubscribed, rather than clicking the link to do so within the system, you can manually unsubscribe them from their contact profile.
Start from Audience & Contacts
Step 1: Click Contacts to open a list of your contacts.
Step 2: Type in the name or email of the desired contact in the search bar.
Then click on the desired contact. A contact profile will open.
Scroll down, and on the ride hand side, there will be information regarding consent and subscriptions.
Step 3: In Channel subscriptions, Click the checkbox (blue) next to Email (or desired channel)
This will manually unsubscribe the contact from receiving email marketing communications.