Installation of WatchMaker on Samsung Galaxy Watch 4 should be automatic when you install WatchMaker from Google Play :

Click the expand icon on the right-hand side icon of the Install button (shown above) to check which devices WatchMaker will be installed on.

In this case it is set to install on Samsung SM-R860 (Galaxy Watch 4) although your Samsung device may have a slightly different model name.

You can check to see if your Galaxy Watch 4 has received the install from this page as it will say 'Installed' underneath your Samsung device.

You can also check for WatchMaker on your Galaxy Watch 4 itself by long pressing on the watch itself and swiping left or right until you see the WatchMaker app.

If the Install option from Google Play did not work you can still install WatchMaker on your Galaxy Watch 4 :

1. Ensure WatchMaker is installed on your phone
2. On your Galaxy Watch 4 tap the screen to wake and then scroll down to see your app list
3. Tap Google Play icon
4. Tap “Apps on your phone”
5. Scroll down to “Watch Faces - …” app with the WatchMaker icon
6. Tap Install

Once WatchMaker is installed on your watch, long press on the Galaxy Watch 4 and swipe left or right to ensure WatchMaker is your active watch face.

You can also set the active watch face using the Galaxy Wearable app - select Watch faces → then WatchMaker.

You will then be able to send watchfaces from the phone app!