App Store reject my app at TestFlight and ask me to do app thinning

I got below message from app store connect.

"Your build number 18 and 20 are not eligible for TestFlight due to no app thinning variant found. Please take a look at the following guideline, and resubmit with higher build number"

May I know how to do app thinning variant and how to upload to TestFlight again?

Regards, Alex

App Store reject my app at TestFlight and ask me to do app thinning
 
 
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