I have successfully integrated my Harmony hub, its devices, and activities into my SmartThings hub. But somehow, over time, I ended up with duplicate Harmony devices in my ST menu. So, I deleted the extras from the ST app. (I changed nothing in the Harmony app).
Now I realize, one of the deleted activities is needed. I can still see the Harmony Hub and other activities. But I cannot figure out how to reacquire access to the activity that still resides and works in the Harmony Hub, but no longer appears in the ST interface.