Find the Google Mobile Ads Application IDs
To get the App ID for your mobile app in Google Ad Manager,
Sign in to Google Ad Manager with the same ID that owns the apps.
Click Inventory > Apps.
Find the mobile app for which you need the ID
Copy the "App ID" to your clipboard.
Find ad unit IDs and sizes
Click Inventory > Ad units.
Click the name of the ad unit for which you want to create an ad tag, or create a new ad unit.
Select the tag type "Mobile Application Tag" and click Continue.
From Tag results, click the Copy Tag
Here is how the ads will appear on your mobile