I did it too.
I found the solution:
You need the desk vertical- ie, in an 'I' position - the 'I' being the desk standing on one of it's smaller sides and standing vertically.
You need to align the top surface of the desk with the steps - ie so it is sliding up the stairs upside down (smoothside down).
You then just basically topple it over from the vertical position onto the steps and Large it all the way.
I found the solution:
You need the desk vertical- ie, in an 'I' position - the 'I' being the desk standing on one of it's smaller sides and standing vertically.
You need to align the top surface of the desk with the steps - ie so it is sliding up the stairs upside down (smoothside down).
You then just basically topple it over from the vertical position onto the steps and Large it all the way.