To manually remove a recipient from a Campaign, first use the Search bar at the top right of the Campaigns dashboard to search by name, email, or domain across all of your Campaigns if you're not sure which Campaign they would be on.
Once your recipient appears, click on the name of the Campaign that they are on and you'll be brought to the Manage Recipients view. From there, select the check box next to the name of the recipient and click the "Remove" button in the bottom right.
Alternatively, if you already know which Campaign your recipient is on, find that Campaign in your dashboard and hover over it, then select the "Manage Recipients" button that appears.
This will then take you to the Manage Recipients view. You can either scroll through to find the recipient you'd like to remove or use the search bar on this page to find them. Once you do, select the check box next to the name of the recipient and click the "Remove" button in the bottom right.
To remove multiple recipients at one time, simply select multiple check boxes before clicking "Remove."