If your Prime License Manager has internet access, you may register it through PLM. There is an option to import license by PAK. If it doesn't have internet access, you can register the PAK at cisco.com/go/license and download the file, then import the license by file.
If your PAK was previously registered to another PLM, then you will have to contact Cisco Global Licensing to re-host the license to a new PLM server.