Motivation: You have an AdMob application that already links to an incorrect Google Play app or Apple Store application. You want to change this incorrect link.
Solution: If the app is already linked, you can’t change it. For Android apps, you can add additional stores after linking.
The only thing that you can do at this moment is to go to Apps > VIEW ALL APPS, then find the correct app you linked, and create a new ad unit for use.