That makes your life a lot easier. Assuming you can drive the stepper from an Arduino this should be reasonably easy I think. Basically you need to figure out how many steps the stepper needs to take to get between positions. I expect a tutorial like this one from Adafruit should get you going
The Arduino code included in there lets you enter the number of steps from the serial console to control the stepper. Once you determine the number of steps between positions, then you can create the code to move to that position when a button is pressed. You likely need to know where the table is now and therefore how many steps and in which direction it needs to go to get to the new position then feed that number of steps to the stepper motor. If you are using the current hardware, you will need to figure out what I/O pins the stepper controller uses and probably modify the Arduino code to make their I/O pins match the ones your controller is using.
edit: A late thought, check if the unit has limit switches to prevent the table from going to far! It is easy to make a mistake in software and tell the stepper to go to far. Without a limit switch you may damage the table. If there aren’t limit switches already installed, I would advise adding two of these
The power to the stepper motor connects to the NC (normally closed) contact. If the table gets too near the edge due to a software error, the switch will trip and remove the power from the stepper to prevent damage to the table.
Peter