I am able to make my app, the device owner app through NFC as mentioned here. Now I want to update my app over the air, but I couldn\'t find a method without rooting
You could use Play Store to provide updates for your app:
Provision device owner app through NFC, just as you already did.
Provide an updated version (same package name, same signature, higher version number) of your device owner app on Play Store.
In the Play Store app on your device, search for your Play Store version of the app and install the update.
Activate auto-updates for your device owner app in Play Store (on the Play Store page of your app, click menu (three dots) and activate the checkbox for auto-update.
That's quite some effort for the provisioning phase, but the device should receive future updates automatically.