HALion Symphonic Orchestra (HSO) and Sonic SE have their own installer routines and function as VST plugins (other plugin types supported as well). They are somewhat separate from Dorico. One can remove or install Dorico without touching HALion, and vice verse.
In fact, you can use these HALion instruments with other DAWs besides Dorico provided you have the most up to date versions properly installed, and your Dorico eLisencer stuff is active on said system.
If you still have Sonic SE 2 installed, it can be updated for free to Sonic SE 3. Simply run the SE3 installer and it will update things. You will NOT need the free key they send you via email since your Dorico key already covers it.
I’m not sure if it was installed with Dorico, but a simple plugin exists to host individual HSO instruments per instance in any DAW. Since I already had HSO, the plugin has long been on my system. With Sonic 3 SE, you don’t really need it, as Sonic 3 SE hosts HSO content just as well (better really). If you need the simple HSO plugin, I think it can be extracted from here. If it’s not an option in the installer, check the extras folders.