Yes, you can do so in the following ways:

Via UI

1. Select Search Contacts.

2. Select Add Rule.

3. Select Channel-addresses.

4. Type the email address in using matches.

5. Then in the upper right menu, select View/edit individual subscriber results.

6. Select the email address.

7. In the Channels panel, select Edit.

8. Select Subscribed then Save.

Via API

You can also resubscribe a contact using the "contacts" POST or PUT API as follows:

{
  "channels": {
    "email": {
      "address": "myname@example.com",
      "subscribeStatus": "subscribed"
    }
  },
  "forceSubscribe": true
}

Please note that re-subscribing a contact may require documentation of the reason and should only be performed in adherence of existing governing legislation. Consult your legal team if you are unclear about your practices and any possible legal implications or violations of modifying a contact's subscribe status.