From the Configuration cog, select "Manage People"
Find the employee you wish to reinstate and click on the hamburger icon on the right-hand side and then click "Activate Account"
In the reactivate dialog, set the user type, desired access level, and whether they can log into Lumia:
Click OK to complete the operation.
What happens next?
The person is reactivated. If selected, they will receive an email to reactivate their account.
Converting between Stakeholders and Employees