This is done via the Gear Ratio settings, specifically the "Motor Revolutions" (object 0x6091 : 01) and the "Shaft Revolutions" (object 0x6091 : 02).
The Shaft Revolutions determines the number of step (pulse) inputs required to move the Motor Revolutions encoder counts.
As an example, see the screen capture below from the Drive Support Tool. This example used a PM-FCL motor which has a feedback resolution of 524288 counts / rev.
With the Shaft Revolutions value configured for 5000, the drive needs 5000 incoming steps (pulses) to move 524288 counts (aka - 1 revolution). If Shaft Revolutions value is changed to 25000 then it would require 25000 steps/rev (assuming Motor Revolutions was not changed).
Note - after changing these values you need to save the values to the EEPROM (Save to Memory button) and then a power cycle for the new values to be active.