If you are an Org Admin, you can invite an existing user to your organization via the Team Management UI in your dashboard. First, log into your Sauce Labs Dashboard and then click on Team Management under Account in the upper right hand corner of your dashboard. Then under the Users tab, click on the blue + on the right.
Here there are 2 tabs.
The Invite Via Email tab provides a way to invite an existing user or a brand new user to your organization. Enter a valid email address for an existing user or a user who has yet to create an account. Choose a User Role (Member, Team Admin, or Org Admin). Select a team for the user if you wish, and then click Send Invite.
After the user receives an email, they can accept the invitation, after which they will lose access to their previous organization if they were an existing user.
The Manual Entry tab allows you to create a new user for your organization. Provide a unique username and password for your new user, and select a Team if needed. Choose a role for the new user (Member, Team Admin, or Org Admin). More can be found on Team Management roles here.
If you are having trouble moving a user into your organization, feel free to open a support ticket here.
In your support ticket, please include the username of your Org Admin, the username of the user you wish to move, the role for the user in your org, and the team to which they will belong.