If someone has been added to the ""Deny List"" how can I take them off that list?

If you can see the Deny List, but you can't find the User in the deny list; then you need to reach out to your QuickBase Account owner.  If you see the Deny List and can find the User, then check the box on the left of the row; and then click the button [Remove from Deny List] which will push them back into the Users list.  Now, they will show up as Users in the Applications.