By default all your users/affiliates can have access to multiple campaigns. To create a special campaign for an affiliate you can follow the simple steps underneath.
Step 1: From your Admin control panel go to "Referral Programs" and click the "Add" button.
Step 2: Here Fill out the necessary information which will be displayed to your affiliates and click on the link saying "View Advance Settings".
Step 3: Now make sure the option saying "Make Available To All Users" is unchecked and then click "Continue".
Step 4: Finish the setup for your special campaign.
Step 5: get back to your Dashboard, click "Users" and click at pencil button to edit user.
Step 6: Click to assign special campaign to this specific user.
And Update to finish the setup.