After folding forward 2nd row seat, to get access to the third row, the seat stuck.

I can not fold it back and I cannot move it on the track. When I lift the handle I can see all the little parts move - but the seat doesn't move.

I suspect something got in the track - although I can't see it. Does anyone have tips on cleaning the tracks or removing the seat so I can get access to the track.

Many thanks for any suggestions.