XM1110_1103886 change Baud Rate

We’ve bought GNSS XM1110_1103886 (Firmware AXN 5.1.1_8252). I can’t change Baud Rate from 115 200bps (default) to 9600bps, using command $PMTK251, 9600*17.

Earlier I used FireFly (Firmware AXN 3.8_8552) and changed Baud Rate to 9600bps, using command $PMTK251, 960017 and vice versa, using command $PMTK251, 1152001F.

Can you please help me?
Thanks in advance.