Unfortunately, currently in PlayHQ, you can only add WWC information at the point of registration. Although you can edit previously entered information from your account/profile, you cannot add it in if you haven't previously added it when registering in the past. This is something we're wanting PlayHQ to fix.
In the meantime, what you can do is commence (but not submit) a registration, By doing so and entering in your WWC, it will save this to your profile, even if you don't submit the registration.
Can you please do so using this form and select volunteer as the role? It's just a dummy registration form we use for situations like this.