Find some flat and level ground, I don't think it is possible any other way, then you should measure the distance between the top of the wheel arch and the ground, or centre of the wheel, for each corner. This will mean your car is level.
I'm sure I've read somewhere what this height should be, something like 760mm, but to be honest you can define it yourself to be pretty close to what it should be because it's going to be your eye that decides the car is sitting at the right level based on how it looks.
The EAS measures heights as 0 to 255 as shown on the computer, and iirc normal height is around 120. Each corner will have a slightly different reading to account for tolerances, maybe + or - 5, you can't enter the same value for every corner as that will make it uneven.
Then you can set the other heights based on the height differences specified.