How do I extract the call recordings from the app?

iOS

If you tap on the info button next to the recording in the history, there is a share option where you can share the file via all the usual methods used on iOS.

But this is of course not easy if you have lots of recordings. In that case, you should use either iTunes file sharing (for older macOS or windows)

https://support.apple.com/en-us/HT201301

or file sharing through finder (through newer macOS versions)

https://support.apple.com/en-us/HT210598

Android

If you tap on the 3 dot menu button next to the recording in the history, there is a share option where you can share the file via all the usual methods used on android.

For volume extraction, recordings can be shared in all the normal ways as well.  The exact location may vary from device to device, but there will normally be a folder for the app under music, then a folder for recordings in that folder.  You can access them from pretty much any android file manager and share them all the ways you normally would from there.