To correct username mapping I had to unassign users and reassign them. For those users I now have a notice, a Task: Auto deprovisioning is not available for this app. Please manually deprovision this account in the app.
Thank you for reaching out to Okta Support, my name is Adrian.
This task stands only as a notification / reminder and it occurs only when a users is being removed from an application that does not support deprovisioning. In other words, even if you removed the user from the application / delete / deactivate the user on the Okta side, the user's account is still active on the application side. That notification is there to remind you that you will have to remove the user from the application as well. Here is our documentation regarding Provisioning and Deprovisioning: https://help.okta.com/en/prod/Content/Topics/Apps/Provisioning_Deprovisioning_Overview.htm?Highlight=deprovisioning%20users
Now, to perform the task, from the Task view, select the checkbox next to it, and push "Mark selected complete, from the next screen keep manually deprovisioned and click "Mark Complete"