https://help.nowtv.com/article/forgotten-login-details @Baggiewba use that link to identify the Sky ID linked to your email and set a new password. You should then be able to sort out applying the Vodafone offer. Any issues as chat. As an aside can I just check you were not hoping to watch on a Youview device? Just only movies are available on that.
Please take a moment to click thanks or marked as solution if this answered your question. I am a community contributor not staff so cannot help you with account matters I can just attempt to point you in the right direction.