From the Organisation tab, navigate to Organisation Design and then click on Roles
On the role page, change the grid to show inactive roles:
Find the Inactive role that you wish to re-activate and click on the dots on the right-hand side to open the menu. Click “Reactivate”
In the confirmation dialog, click the "Re-activate" button.
What happens next?
The Role will now appear as Active and people can be assigned to it.
Note: if you have filtered the grid by 'Inactive' roles, then you will need to reset this filter.