Where are my songs stored on Android?

It varies from place to place on different phone manufacturers, but is usually in

/Android/data/com.elf.koalasampler/files/songs

On Android 11 and above this folder may not be accessible from your phone, but it should be from your computer – on Mac, Google make an app called Android File Transfer which will let you access this folder. On windows, you should be able to access it in Explorer.