To be perfectly honest, there may or may not be a quick release button. On my 190E, I actually removed the seatbacks to get at the headrest so that I could get a better look. I had some good reasons for this:
1. wanted to tighten the cargo netting (very easy with seatback removed)
2. wanted to investigate a broken power headrest link on the right (easy fix thanks to some advice I found here)
3. wanted to see how the mechanism worked and really clean the seatbacks well (much easier with them removed).
Removing them is easy. There are 2 screws on the bottom of the seatbacks. Remove them and slide down on the seatback. It will pop right out of the seat and you can get to everything.
So, since I don't remember if there is a manual button or not, there might be compelling reasons to pop the backs off anyhow. You will see how to adjust/remove everything.
Happy Motoring and Welcome! This is a great site.
John J. Meadows
'85 190E 2.3L 99k mi.
'83 300D Turbo 268k mi. (sold to Mom and Dad for a song)
1L - TCW Law School, U. of Richmond