How do I undo this connector? (1/2 BSI)

[SymonAncymon]

Hey, I've got a leaking toilet and I need to replace the filling valve device which is a Geberit 810.L3 Type 340 with a 1/2" connector. Problem I've got is the connection under the tank (image attached). The top plastic nut (yellow) is only to hold the fill valve in place - I can undo it by hand.
I believe I need to undo the second plastic nut from the top (purple) but the access is very limited and can't undo it with my hands (rotating direction as per blue arrow) or squeeze in any tool...
Am I after the right thing? Or am I doing something wrong? Is the green sleeve some sort of quick connector?

 

[SimonG]

You'll have to undo the purple first before undoing the yellow.

 

[SymonAncymon]

You'll have to undo the purple first before undoing the yellow.

Thanks. So I guess I need to tighten up again the yellow and keep trying to undo the purple? (it rotates the entire valve within the tank which makes it even more difficult to unscrew)

Edit:
Oh dear...I managed to loosen the purple nut but it rotates with the entire hose... So I can't fully undo it without undoing the hose at the supply valve.

 

[Lou]

Oh dear. I hope you manage to get things sorted out!