If you deactivate a member’s account, you have the ability to reactivate it. Reactivating a user's account allows them back into the platform and any Groups they were still an active member in.
Open Org Admin Page
To reactivate a Member from your Organization, select the Organization Administration icon from the top of the page.
Under Actions, select the Reactivate button associated to the Member you would like to reactivate from your Organization. The Member is now reactivated.