How to set the temperature in a refrigerator without proper indication on the dials?

First, figure out the temperature that you want to run the fridge at (35-38F is standard). Then, buy a refrigerator temperature gauge.

Work the dial up or down accordingly until it's where you need it. The dial can even have worn off numbers, and this method will still work.

I can't tell from your question whether you are asking what temperature you should set your refrigerator to or asking how you go about setting it to a different temperature. The answer that Grey Dog provided is correct concerning the target temperature.

In case you were actually asking HOW to change the settings, let me add this - if your dial has numbers without any indication of which direction gets you to a colder setting, then probably a higher number represents a colder temperature (higher number, lower temperature - that seems stupid to me but they don't pay me to design refrigerators) - if your dial doesn't have numbers or any indication of which direction gets you to a colder setting, then probably turning your dial clockwise gets you to a colder temperature (again with the turning it up to turn it down). These directions are not universal, but they have been common to many models for many years.

Note - once you change the temperature setting of a refrigerator or freezer, it might take as long as 24 hours for the temperature to stabilize enough for you to get an honest thermometer reading.

Another way to know for sure which direction for your dial is warmer/colder is to listen to your refrigerator as you turn the knob all the way in each direction - since the refrigerator compressor starts-up to cool the refrigerator down, the direction you are turning when you hear that compressor initialize is the direction of "colder."