An oscilloscope displays the input signal. It does not modify the signal in any way, including its frequency. No amount of tuning would change the signal. The only changes are how the display is scaled.
To read the frequency of the signal, you adjust the time/div setting to capture at least one period of the signal, then count the number of divisions this period spans, then multiply this by the time/div setting.
For example, if your signal period stretches 2 divisions on the display, and the time/div setting is 50ms/div, this means that the period is 100ms, or 10Hz.