Need to set up a SSID at only 24G, any clue how?

[balaji.bandi]

what kind of deployment, is this AP managed by WLC or AP is Autonomous mode ?

some guide lines of config :

https://www.cisco.com/c/en/us/td/docs/wireless/access_point/15-3-3/configuration/guide/cg15-3-3/cg15-3-3-chap4-first.html

[Tony Rosolek]

Which software version do you use? Is it standalone or controller based? 

On IOS-XE you can configure it in the WLAN profile -> General -> Radio Policy