To change the UHF frequency digits to the right of the decimal, what must you do?

To change the UHF frequency digits to the right of the decimal, pulling out the small knob is the correct action. This small knob is designed specifically for adjusting the frequency settings in fine increments, which allows for precise changes to those decimals.

By pulling out the small knob, the system enters a mode that enables the pilot to make adjustments to the finer aspects of the UHF frequency. This is essential for properly tuning into a specific communication channel when operating within the aircraft systems, ensuring clear and effective communication.

The other options would not achieve the necessary adjustment to the frequency. Turning the large knob typically adjusts the whole frequency up or down more broadly rather than affecting the decimals specifically. Pressing the reset button is meant to revert the system to its default settings, which does not facilitate frequency changes. Flipping the frequency switch generally alters between standby and active frequency but does not isolate or modify the digits to the right of the decimal.