Vocal channel return

[brs]

Using a 4 channel Amp from Guitar Center (Acoustic brand, their own brand), which has a signal send on the back to output to a Monitor speaker. I have my Korg keyboard using 2 of the channels and the 3rd channel for my vocal. Wanting to know if there is a way to only return (send) the vocal to the monitor amp., in other words, separating he vocal from the combined keyboard/vocal signal. Thank you.