Company admin and managers have the ability to reactivate inactive users. Users who were once active will appear in the 'Inactive' section of your 'Manage People' page.
Success Center article 🗒: How does adding/removing users impact billing?
Note
If you have SCIM enabled in your account, the instructions below will not work for you. You will need to reactivate the users in SCIM.
Reactivate a user
1. There are two ways to get to the Manage people page.
Option #1 Click on your avatar in the upper right corner of your page and then click 'Manage people'.
Option #2 Click on 'Settings' from the left navigation.
Then click on 'People' to expand the people settings.
Last, click on 'Manage people'.
2. Click on the 'Inactive' tab.
3. Inactive users will appear under the 'Inactive people' section. Find the user you would like to reactivate.
4. Once you click 'Reactivate', a notice will show up and confirm their account was reactivated. 
See these articles to update the employee's reporting frequency, reporting day, and reviewer.