https://www.gtx970settlement.com/Home.aspx
All you need are some sort of identification number (Device ID’s the easiest since you can get it via Nvidia Control Panel) and optionally a screenshot of a receipt or something.
Deadline’s November 30th, but you won’t be getting your $30 until December.
Also PCGamer article link for genuineness: http://www.pcgamer.com/heres-how-to-claim-your-30-nvidia-geforce-gtx-970-settlement/