adding my two cents I wasn't able to connect as long as I had the Yunmai app, so I did this and now it syncs instantly and automatically.
Do not use the Yunmai app.
If you already did, remove the batteries from the scale and uninstall the app, then do this:
Put batteries on the scale, step on it and look for it from the bluetooth menu of your phone, connect to it and enter 000000 as the passcode, now go to the S health app and add it as an accessory you'll see that this time it detects the scale.