I just purchased a Pro license so that I can use the plug-in on a few more sites. I have an “Active” Starter license on one site with a warning that says it’s an “unlicensed plug-in.” I have 12 forms built on that site and don’t want to lose them if I add my new Pro License key. Should I be worried?!
You can change the value of the license key setting at any time, it has no impact on your forms. The license impacts access to updates, and which add-ons can be installed via the Forms > Add-Ons page.
Try removing the old key saving the settings, then reload the page.
If the input remains empty, add your new key and save the settings.
If the input is repopulated with the old key, that indicates it was hardcoded, probably by the host. In that case, try manually reinstalling using the zip from your Gravity Forms account downloads page: How To Install Gravity Forms - Gravity Forms Documentation
The expiration date is missing in the screenshot. Have you installed a nulled/cracked copy on the website before?
If so, you can follow @richardw8k’s instructions to reinstall Gravity Forms manually. This should fix the issue without losing any forms or submission data.