You may be able to this from the shell of airwave - do you have access to that (some do, some dont). Alternatively, I have done this previously (to monitor the effect of 3dB power decrements in 2.4ghz on 5ghz usage) by using a script to run "show ap association | begin Num" and then parse the result into CSV, and then plotted it in excel. Could that be an option?
Num Clients:25
Total num of 5G capable clients:24
Total num of 5G capable clients in 2.4G band:23
Total num of 5G capable clients in 5G band:1
Total num of 2.4G only clients:1