In most cases, when a new license for an add-on is purchased, the new license key can be retrieved from Atlassian. Replace the trial license key with the purchased one in the Manage add-on configuration page.
The evaluation license key is automatically configured upon the first installation of the Git Integration for Jira add-on.
Log in to your My Atlassian Account where you will see the purchased license. From there, you can find the key:
Go to the Git Integration for Jira add-on configuration (Jira Administration > Add-ons > Manage add-ons).
Click the Edit icon to enter/change the License key.
If the License key field is blank, you need to obtain a license for the Git Integration add-on. Click Buy now or Free trial. Login to your Atlassian account, when prompted, to acquire the license based on your selected license mode.