If you want to publish a new app in the Play Store, you need to decompile the AAB and set targetSdk = 30 (because you must use AAB from August 1st for new apps).
As far as I know, there is unfortunately no (generally) working tool with which an AAB can be decompiled.
If you want to release an update in the Play Store, you can do it as usual (without changing targetSdk or anything else, until the end of Okt).