What you mean by "each channel"? ZED24 is a mixer. Build-in USB interface has only one stereo input/output (or 2 mono), see the page 24 in User Guide. To record 2 mono tracks instead of one stereo, select corresponding Mono input (Left or Right) in the "IN/OUT" section (it is shown in the second picture on page 24).
In case you have armed several tracks with the same input, they all record the same material.