Here are all the steps necessary to make OTA update possible after creating a new product in your android things console :
1 - Create your first build configuration, either from the empty bundle in the console or from a personnal bundle you added.
2 - Download build of this build configuration. You will get an Android Things image. Flash it to your RPi as you did when you flashed the Android Things regular image. https://developer.android.com/things/hardware/raspberrypi.html#flashing_the_image
From now on, your RPi will check if a different version of your product has been pushed from the console. The check happens every 5 or 6 hours so you might have to be patient. Also your RPi needs to have internet access.
3 - Upload another bundle to your console, create a build configuration for it and then push it to your devices via the OTA updates panel of your console.
4 - You will need to manually reboot the RPi to apply the update.
This article from Dave McKelvie is a good example in my opinion : http://android.geek.nz/hello-android-things-developer-console/