Thanks to this menu, you can configure one of the RC switch and assign them a flight mode. In order to use it, you need to assign a switch of your RC to the channel 5. Typically, it is done with the RCs mixer/auxiliar channel setting.
Once you have done this, simply move the switch of position and check which PWM ranges is taking. Assign this PWM ranges to the flight modes you want to have.
Note that the menu enables to configure six flight modes, but, normally, the RCs only have 2/3 position switch, which makes impossible to use all the flight modes. You could try to make an logic operation between two switches in your RC in order to achieve a six level logical mix.