Always back up your license before performing major hardware maintenance. You can use the export tool in the web interface to save your current XML file to a local drive. If you lose your license and cannot find it in the locker, users on Spiceworks Community suggest contacting Dell support with your Service Tag to have it resent. Key Advanced Features
Once you have obtained an iDRAC9 license key, you need to activate it on your server. Here's a step-by-step guide: idrac9 license key