On the Viu web page, you can set a new PIN by hovering over your profile picture on the top right of the homepage. Click My Profile > My Devices > Enable under Parental Controls and you will be able to create a new PIN.
In the Viu app, you can set a new PIN by tapping the Viu logo in the top left corner to enter Member Center. Tap Parental Controls > Switch on Restricted Content and you can create a new PIN.