Daihatsu Charade rear seat removal


Info needed on rear seat removal on charade 1.0 I have unhooked the 2 rear clips and pulled the seat forward but the front fixings go through the carpet and into a square white plastic plug that is fixed through the floor. I suspect that this is some kind of a "popper" but i,m reluctant to exert any force on it as it just might be bolted from underneath the car! Can anyone please advise?