To open it you'll need to climb in the back and unscrew the plastic boot trim,
then pull/push the metal bar that actually locks it.
But in terms of fixing it, a trip to Renault is in order to get a new dohicky,
you're best off talking to Adam at Wolverhampton Renault, he's a trader on here and will know exactly what part you'll need,
plus it's usually delivered within a week.
When mine broke it was permanently unlocked, so at least your car's secure.