Currently there is no way to create an App using the Marketing API's. What you can do is add Ad accounts to a Marketing API so that the app can make API calls to it. You can add 5 Ad Accounts to your app if it's a Dev tier app, 25 for Basic tier and unlimited number of Ad Accounts for a Standard tier app.
Here is how you can add an Ad Account to your Marketing API. In your app dashboard, go to Apps > Settings > Advanced. Under Advertising Accounts click Marketing API. The account configuration tool opens. Enter in an account ID. You should enter a numeric value; do not include act_ from the account ID. Check the account IDs match exactly. When you reach your maximum, Add is disabled.
Once you have added Ad accounts to the Marketing App, what you can do is use a System user to make API calls. You can generate an access token for the system user and use that to make API calls. Here is a link to a document that explains how to create and make API calls from a system user.
https://developers.facebook.com/docs/marketing-api/businessmanager/systemuser/v2.9