The changes can be made from GUI only on APs accessed via the Enterprise UI. They are not available for APs accessed via Swift UI (also called Express UI)
Assuming you are accessing the AP using the Enterprise UI:
Go to Configuration > Devices > Device Overrides > Double click on the AP in the list > Expand Interface > Radios > Double click on the Radio you'd like to hide it on for example Radio 1 > Radio settings > Antenna Mode > select your choice from the drop down menu > Ok > Exit > Commit and Save.
The above is configured as an override; however, it can also be configured as a system profile setting should you have multiple APs adopted onto a controller or a virtual controller.
I hope this helps,
Regards,
Chris
Christoph S.