PRI hasn't required license for several years, so must be pretty old software version, probably pre-4 as I recall. The dealer who controls their account record must sell them the license, because you'll need to upload new license that includes PRI. They'll need the license number from HELP/ABOUT SOFTWARE LICENSES. Newer versions call it APPLICATION RECORD and HARDWARE ID.
Older versions licensed by the unique number on a USB key, newer versions use the SN from the flash card and tie it to an app record number at Mitel.
Since you need new license any way, good time to upgrade to current version...I think you'll get PRI and lots of other features free.