RIBbench seat fitting

[Pompier64]

Hi Everyone,
I removed the bench seat of my RIB bed to get it upholstered. I can't fathom out how to replace it. The brackets take ages to get in line then when it's fixed back to the frame it either won't move or does move but grates against what I imagine is the ratchet mechanism.
Any ideas please?
Ta.

 

[Handyman]

I've not come across this. I have a RIB seat bed that was reupholstered and the brackets just went back in the position they came from. The lever mechanism could have been lifted which maybe could have unwound the tension on the spring thus causing a problem, but not too sure.