I was taking some parts off a breaker the other day and wanted the boot rubber.
The battery was dead so could not get the boot open, after sitting inside the boot, back seats down i managed to remove the parcel shelf, then the plastic trims around the window before partially removing the tailgate trim.
But once inside i could not get the tailgate open, there is no cable for a manual release, it's all electric.
If the parts are faulty i'd say it's a dealer job.*
*The breakers had the key and a battery pack so this was the only way to get it open.