On your campaign settings, under Campaign Users, you can add assign users to your campaign.
But first you need to create these users here: https://account.seoreseller.com/settings/users ( click on your profile picture on the top right of the page, then select Manage Users)
Click "Add new user" to create a new user. You will be asked the email, username, role or password of the user.
Employee vs Client users
An Employee user has access to most of the dashboard features via your white labeled dashboard. You can activate and deactivate access features by editing its profile.
A Client user has only access to the reporting dashboard to see the progress of the campaign.
Employees count is limited based on your Agency Tools plan while Clients are unlimited and free.