Trying to change setting on AT&T Nighthawk M6 Pro to mixed wireless from 802.11N ONLY

Can't find that particular setting. I'm being geeky and trying to get a discontinued Sony Dash alarm clock to connect to 2.4 wireless.

Per internet research the retired Dash only supports 802.11B and 802.11G... but it is well pre-802.11N

Can I change this setting somewhere or is it not even an option on the M6 Pro?