What version of HALion do you have?
Full H6?
Full Sonic 3?
Sonic SE, and content that comes with a Steinberg Host (Cubase/Dorico/Nuendo)?
If you’ve got a full version of HALion 6 or Sonic 3…
Use your OS app manager to remove H7.
Using the Steinberg Library Manager, remove any libraries that you might have updated.
Reinstall H6, and reinstall the old H6 content. Get it all and reinstall if you’re running a full version. If your content came with a Host, download the exact content that was provided with said host/version, and reinstall it.
You can bypass the Steinberg Download Center and grab specific installers here: Downloads | Steinberg
Make sure the latest version of eLisencer is installed and your dongle is plugged in.
Hopefully that will sort things for you.
It gets confusing lately because of a newer database. The base content/libraries have also been redone since H7 (different organization, and new Macro editors).
When H7 first rolled out, I could mix and match the dongle ware with the new stuff, but over time it seems like the best way to go is stay with an all eLicenser setup (Cubase 11/Dorico 4), or upgrade everything Steinberg to versions fully compatible with the Download Center (HAlion/Sonic 7 with Cubase 12/Dorico 5 or later), the new Activation Center, and the latest versions of the Steinberg Database (MediaBay).
If you don’t use a Steinberg host at all, it’s a little less complicated (the database thing), but you’ll want to avoid updating content libraries to the newest stuff. Stick with content that shipped with H6, or is meant to be unlocked by the older eLicenser system. Extra content on the new Activation center should work, but be careful when ‘adding it’. Manage it with the Steinberg Library manager, and don’t upgrade the player to Sonic 7 (stick with the last HSSE 3.5.10…the one that works with both eLicenser and Activation Manager, and you can get it from this Dorico 4 support area.).