here is video tutorial
But it’s made for standard android devices. You said, you don’t have back button. I use back button for showing “General settings” from where you can edit your game layout.
This process will be simplified in next version, but still needs back button, because it calls menu options.
Has your smart watch any special buttons? Maybe I can re-bind “back button” to something else.
Edit : Another option is made key layout on standard device and then import it on watch. The buttons are saved in percentage values, so buttons proportions will be scaled. Well, there may be problem with another screen aspect ratio, but with some effort it could be done.