Where: This change applies to Lightning Experience, Salesforce Classic, and all versions of the Salesforce app in all editions of Salesforce with any Pardot edition.
Who: Pardot admins enable this setting. Pardot admins and users with the Toggle Opt-in Status permission can opt prospects back in from Pardot. In Salesforce, users with the appropriate field-level permissions can opt in leads and contacts.
How: In Pardot, edit your Salesforce connector, and select Overwrite Prospect Opted Out field. Accept the terms, and then save your connector.