A Cluster can be licensed following these simple steps

Step 1 is to download a Cluster Summary File(CSF)
On your Prism home screen, click on the Gear Wheel (top right of the screen) --> Licensing --> Update License -->Download.
The CSF will be generated

Step 2 is to generate a License Summary File(LSF)
Login to your support portal account and continue with the steps below
Click on the Menu Icon ---> Licenses --> Licenses--> Manage Licenses --> Upload the CSF. Based on the product for which you are applying the license(AOS, Files, Prism Pro, Flow, Buckets etc), select the License type from the cards visible and click on Next, then download which will generate the LSF.

Step 3 is uploading LSF to the Prism 
Access the Prism Console, under the Licensing page, Upload the LSF and click on Apply License, the licenses will be updated now. 

Note : Refresh(logout & re-login) the Prism for the licensing changes get applied.