Hi,
I believe you will have to setup the trial license for this setup and as you already have dev/test lab you should be able to configure this. [https://learn.microsoft.com/en-us/microsoft-365/security/defender/eval-defender-endpoint-enable-eval?view=o365-worldwide
Also follow this YT link - [https://www.youtube.com/watch?v=4x7NDxdEo94
Hope this helps.
JS
==
Please Accept the answer if the information helped you. This will help us and others in the community as well.