This works and it is all thanks to u/GRRemlin on Reddit. I have just gone through these steps and I now have 14 of my downloaded watchfaces showing on the Galaxy Wearable app and I can now customize my watchface from the app.
These are the instructions, copied & pasted from his post...
"1. Write down all the names of the installed watch
faces.
2. Uninstall them from the watch (tried several from the watch face selection list and several from the playstore watch app)
3. Play around the Play Store app on the watch a little to make sure the Uninstall info is synched up to the servers. I usually just open a few app listings, enter the app settings then go back into the Manage Apps section. A good way to check is to open the watch face in the Play Store on the phone and check that it doesn't say that it`s installed on the watch.
4. Force stopped the Galaxy Wearable app on my phone and opened it again. There should be nothing in the Downloaded section.
5. Scroll down to the "Get more watch faces" and clicked it so it opened the Play Store
6. Search for the watch face, make sure that both Phone and Watch are available for the install (should have the selectable checkbox on each) and hit install (MAKE SURE THAT BOTH PHONE AND WATCH ARE SELECTED). Get a notification that the app will be installed on phone and watch soon.
7. Either wait a little or check the Play Store on the
watch to make sure the watch face says installing or installed.
8. In about 30 seconds the watch face shows up in the Downloaded section of the Galaxy Wearable app AND it's fully customizable, complications and al! I even noticed that some previous customizations I've made before uninstalling were retained!
9..
10. PROFIT!
Like I mentioned above, I am cautiously optimistic because I read posts where watch faces disappeared from the app after a while (?). But it might be worth a try.
EDIT: After fully customizing the watch face via the Galaxy Wearable app and applying the change, I tried uninstalling that watch face's companion app from the phone. The watch face STILL shows up in the Wearable app and on the watch!
EDIT #2: I just tried initiating an install of a watch face I've never installed before directly from the Play Store app (not via the Galaxy Wearable app) and the face showed up just fine. I think the main takeaway that both phone and watch versions need to be installed initially rather than just the watch one."
And just a little more info. I only uninstalled all my watchfaces from my watch. They were all still installed on my phone. When I installed each watchface back on my watch, they miraculously appeared in the Galaxy Wearable app.
