I have tried a lot of things and nothing helped (including through mail) except one thing.
If you have a Mac, you can create any voice memo on your watch and then redact it using the Voice Memos app on your Mac, then you should use an app called Loopback (it’s pretty easy to use) to stream audio from anywhere you want (don’t forget to choose Loopback as your microphone in settings).
Then just start replacing your recording and play your audio file, after that, you can easily cut the recording so I would recommend waiting a bit before and after playing an audio file to ensure that everything will fit in.
Maybe it’s not a very convenient way, but it’s the best I could find because you lose nothing in terms of quality unlike if you just recorded the whole song (in my case) directly on your watch.