A Bundle ID, otherwise known as a package which identifies applications in a store. It needs to be unique so that when you upload it to store, it identifies and publishes your app using the package name as the unique app identification.
You can change the Bundle ID in your app settings on the Appodeal website. This field is only editable if no ad requests have been made before. In the case that requests have been made, it’s impossible to change the Bundle ID because it can cause internal working issues with the networks. Instead, you should remove the app that has the incorrect Bundle ID and create a new app with the correct ID. Then you should change the old AppKey to a new one within the app code.