Final answer:
To switch between the frequencies set in COM 1A and COM 1B, use the frequency select switch.
Step-by-step explanation:
To switch between the frequencies set in COM 1A and COM 1B, you should use the frequency select switch. This switch allows you to choose the desired frequency for communication. The COM 1 and COM 2 switches are used to select the communication radios, while the volume control switch adjusts the volume of the audio.