I have these radios and use this software. You want channel 28, which is repeater 6 (RPT-6). Set the input tone to 141.3 and you are good to go.
As Steve mentioned, the manufacturer has apparently locked the channel frequencies to maintain certification, but you can select the tones.
The OP (Crash1) can do similar, with whatever channel/freq/tone combination corresponds to the repeater he wants to hit.