Hi and welcome to devnet forum
There is another thread about generation of 32- and 64-bit APKs in parallel https://forum.qt.io/topic/102625/build-32-64-bit-apk-using-qt-creator/5
Basically you shall have two different toolchains there. One for 32-bit and one for 64-bit Android applications. When you create the APK-bundle through the respective toolchain all shold be automatic.