Usually, if there is a selector switch to match electrical requirements of a monitor or computer to that which may be available in the home, it is for voltage or voltage AND frequency. Seldom is there are selector for frequency only (I've yet to see one anyway).
The selector switch it typically found near where the AC mains power cord enters the enclosure. This can be on the monitor itself - or in the case of a monitor that uses a low voltage cable and connector connected to a power adapter, it would be located on the power adapter instead. Sometimes, these devices automatically detect and switch to match the power being supplied to it. The device should clearly indicate that it will work a wide range of voltages - do not assume it will if it does not specifically indicate that it will.
The selector above is set to 230 volts.
Set the selector switch BEFORE connecting to the power outlet. Most times, the selector switch has the voltage indicated on the slide. The switch will allow the user to choose 110-120 or
220-240 volts. The 110/120 selection is likely to be the 60 Hz variety and the 220/240 selection is likely to be 50 Hz.
If you are unable to locate such a switch, the device is not intended to be changed by the user - and there is likely no "easy way" for the user to change it.
Please rate this reply - good luck!