Looks like you need a small hub puller. Here are the instructions :
Activate rear window wiper to situate it in park position.
– Disconnect battery
– Raise cowling of rear window wiper and detach.
– Loosen hexagonal bolt, but do not remove completely.
– Apply tool T20177
– Raise wiper arm and separate from cone using lateral movements.
– Unscrew hexagonal bolt and remove wiper arm.