You may have users in an application who for various reasons have usernames other than the ones OneLogin uses by default. Do note that this option will only appear when the circumstances allow it; otherwise the button will be hidden. To match those local users with an application’s users, navigate to the Apps > Application In Question > Users. Here you will select Unmatched Users to display the list of users that are currently using the app but do not exist within OneLogin.
Selecting a user here will bring up the Resolve Unmatched User pane. This will allow you to either Match the User in question to an existent user in OneLogin, Create a New User to be matched to the unmatched user, or Delete the User altogether. You can use the field to search for a matching user through all users currently within the account.
Depending on your approval settings, you may have to go to Users > Provisioning to manually approve this task.