You will find the place to change your App ID in the App Store optimization tool panel of your App:
Once you are on the App ID panel, you can read why it's important to have good package name and Bundle ID in your App:
The Package Name (or App ID) serves as a unique identifier for your app on the App Stores. It is part of your app's URL on GooglePlay. Google uses the words in your package name as search keywords, so choosing the right package name will help your app appear on top results when people look for similar content.
- Package names must follow a few rules like:
- The name should be unique.
- The name may contain uppercase or lowercase letters ('A' through 'Z'), numbers, and underscores ('_').
- The name may be formed by parts separated by dots (com.companydomain.appname). However, individual package name parts may only start with letters.
You can change the end of the package name from the HOME subscription and you will be able to change the company name in the Agency subscription.