What you're looking for is a License Warnings Reset Key, and if you're using a 10GB Developer license or 50GB Dev/Test license you'll need to reach out to email@example.com - typically we are able to reply to requests for these within 2-3 business days at most.
Once you've received your Reset Key, just apply it to your Splunk Enterprise deployment like you would any other Splunk Enterprise license.
Adding a valid license does not clear a license violation condition. You need a special not-really-a-license clear-violation license that you can get from your Splunk account team. Or you can save off or otherwise protect your index, uninstall Splunk on your Indexers, reinstall Splunk, then install your license.