Just restore the watch to the original state when you first got it. Then it says that you should connect to a phone but you press the "?" To the left of the language button. Just follow the installer and it should ask you to login to the Samsung account.
In my case the trick was to also completely remove the programs from the phone (but clearing the cache should be enough as well, I think). But then the watch-based store doesn't have all the same apps that the phone based one has. In fact, it doesn't offer the ones that I counted on the most :/