There are two options. The first option is to re-invite them (works on both the Listrunner web and mobile apps) and the second is is to reactivate them through the User directory (only available on the Listrunner web app).
For the second option, follow these steps:
- In the User directory, select the 'Deactivated' tab.
- Scroll to the specific person whom you wish to add.
- Click 'Activate'. This will move that person from the Deactivated list to the Active list.