PSR 970 - singing to an external backing track

[AK]

I have recently purchased a PSR S970 and quite please with it.

Tried to record a song using a backing track in a usb stick but could not get a voice mixed recordin through either of the recorders.

I am quite new to this setup and could be just asking a dumb question but can someone try to explain how it can be done please ?

All I a trying to do is playing a backing track from a usb, adding a beat from the 970 and at the same time mixing voice from a microphone.

Thanks