"apk → android app bundle" easiest convert method?

I finally made app and built apk file by appinventor.

But I need "android app bundle" to register.

I want to know the easiest convert method ("apk → android app bundle" )

I've met some difficulties at the end.

I think it's not possible to create an aab (android app bundle) from an AKP, but APKs from an aab:
android app bundle → APK(s) using bundletool .