I had this problem when I first tried to lower the backs of the rear seats.
There isn't much too it really, but pulling on the lever. Having said that, when one pulls on the lever it does feel as though it will break. But I haven't broken it yet.
So here is how I do it. make sure the seat belt buckles are stowed in the recesses in the seat backs. This is so it won't crease the seats. No need to lower the head rests, there is usually enough room behind the front seats. Gently pull on the lever on the seat back you wish to lower. The lever will reach a false stop. It is as this point you will feel it is going to break. Take courage and pull a little more, and at the same time gently pulling on the seat back. The seat back should lower, without the lever coming away in your hand.
It is VERY unnerving the first time you do it, and it don't get any easier. I have had better rear seat levers than those on the Captur. I guess I will just have to get used to it.
Good luck - I take no responsibility if the lever comes away in your hand.
Edited by: crossbow