Well one way to do it super easily would be to blue tooth your phone to the model 12, send the Bluetooth to track 9/10, set track to “live”, arm the track for record and then play the clip on your phone while recording on the 12.
not sure if the quality of the sound will take a hit due to blue tooth- but You Tube sound quality is already low...? This is just super fast. I do it with drum tracks or metronome app to start a song writing session.
I believe you can record DAW’s output via USB on track 1/2 (set to PC)... again you’ll probably have to actually trigger your DAW to play the clip of interest while arming record for that channel on the Model 12 and letting the clip play
the golden rule is that the Model series MTR is really like a old school tape recorder... it captures what gets played through it (yes there are ways to work with the track WAV files via USB...but for the most part the main workflows within the Model 12 itself are best imagined as actual “recording to tape”).