If you have installed your product without any command line, then it is installed as a trial version.
To activate your Volume License, run the following command line as an elevated administrator:
AdminTool.exe /vl /activate VOLU-MELI-CENS-EKEY /users unlimited /edition Enterprise /supportyears 3 /comments "This is a comment"
This command takes the following parameters:
(if you like using command lines and are wondering what other command lines are available, please go to this specific documentation)