Hello,
Welcome to Microsoft Q&A!
I'm sorry to say that currently, there is no way to let the previous users who brought your apps get your new app for free automatically. You have to record these users on your own.
My suggestion is that you might check the app license in your old apps, once you found that the user had purchased your app, then you could send them a promotion code that could get your new app for free.
Thank you.
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