The green button is the memory button. 1 & 2 button allow two different settings for two different drivers.
The following is taken directly from my 126 owners manual:
"After the seat/head restraint/steering wheel are positioned, push memory button D, release, and within 3 seconds push position button 1."
If you wish to program seat settings, etc. for a second driver, follow instruction in preceding paragraph, only this time depress button 2.
Instructions on a previous page indicate that you should turn key in steering lock to position 1 or 2 with drivers or front passenger door open. I believe you'd do this before setting the position of seats, etc.