Have you downloaded the audio onto your iPhone (from the Merlin app) or are you streaming the audio and wish to capture it?
If the audio file has automatically downloaded onto your phone then it'll be in a default location - these 'locations'
can be hard to find.
If you locate it then you can edit within your phone's audio app.
Another way to capture an audio recording is to stream (play) the file directly from the app whilst simultaneously having an audio recorder app open recording that audio - the audio recorder should capture what is being played.
If the audio recorder doesn't capture what is being played then you need to change its settings for its source recording.
Once captured, you can then edit it as usual within the audio app and then copy/move/upload the file.
And another way is to capture the recording on another phone (iPhone or android) or recording device (laptop audio device) and go from there - the only caveat being that the audio quality will be drastically reduced, but if that isn't a problem then.
If I'm telling you how to suck eggs and you have the file but cannot crop it then feel free to send it to me and I'll have a look/listen