There are three ways you could have installed it. 1) Part of the Halion 5 install. Or, you purchased it and 2) received the disks 3) got a download link.
Re-install Halion 5
Use the Halion Sonic 2 media, not Halion Sonic
Find the downloaded media from the original link and use it
Should you not have the downloaded installer anymore, open a support request with support to have a new link sent to you.