Is there a way to change the frequency/channel on the set?
No. The M300/M700 use frequency hopping to allocate channels (120) and timeslots to each available frequency band.
1880 – 1930 MHz (DECT)
1880 – 1900 MHz (10 carriers) Europe/ETSI
1910 – 1930 MHz (10 carriers) LATAM
1920 – 1930 MHz (5 carriers) US
If for some reason you are having an issue with interference you should try to isolate the source and move the base away from it.