You can re-approve an affiliate as follows:
1. In your Affiliates Overview, Click on the filter Active Users, and set it to Archived.
On this page, you will see a list of affiliates who have been disapproved from your program.
2. To re-approve your affiliate, check the box next to their name. At the top of the page, you'll find the option to Approve for all programs (or Add them to a different program).
Affiliate is in multiple programs
If the affiliate is part of multiple programs and you'd like to re-approve for a specific program, then you could go to their details panel and click on the program status.
A drop down menu will open and you can change their status within the chosen program.
Note: If you want to delete an affiliate permanently, please check this article.