I think Triebwerk, Dark Planet, etc. were originally CONTENT that worked inside of Halion Sonic SE. I see in the Steinberg shop that they are now standalone instruments but the version included as a demo on your disk may still be the old version that needs to be used in Halion Sonic SE.
If this is the case, I assume it works similarly to my Halion Symponic VST Sound in which you just select one of the patches and it loads the GUI for that “instrument”. Last thing to check is the installation folder or your documents folder. Perhaps there is a manual that the installer put in there.
Oh yeah… Your demo license should be a FULL license for a limited time so you may be able to UPDATE to the new standalone versions if desired.