1. First, make sure you are logged-in to your account.
2. Click on the dropdown menu on your username at the top of the page, and then click on "My Profile."
3. Once you're on the "My Profile" page, click on "Messages," and then "Ignore List."
4. Once you're on your Ignore List page, select the user you want to un-ignore by ticking the box before the username, and then click on "Remove Selected."