In the Install SCCM 2012 we have gone through the process of installing a trial version of SCCM 2012 R2 which will be fully functional for 180 days as indicated on top of the SCCM Administrator Console
In order to import the SCCM License key as part of the post installation tasks you will need to either specify it during setup or re-run setup in Site Maintenance Mode once SCCM has been installed.
From the Start menu navigate under Microsoft System Center 2012 R2 category and launch Configuration Manager setup in the first page the Setup wizard will display some useful information to carry on recovery tasks just click on Next
In the following page select Perform site maintenance or reset this site and again click on Next
You will be prompted to accept Microsoft License terms and a configuration task will start
The task will take only a couple of seconds, clicking on the View log you will be able to verify the SCCM License key installation has gone wellIt is worth noting that the above procedure should be performed logging to the SCCM Server with the user account that has been originally used to install SCCM otherwise you could get an error about setup not being able to update SetupInfo SQL table.