How to register for a Free Retrofit solution for my 2 Xbox 360 Wireless Racing Wheel I own?

That warning came out in 2007. Microsoft don't even support the Xbox 360 any more and it's many peripherals. So there is no chance now of a retrofit. The only thing you can do now, if you're worried about the hazard, is to stop using them.

On 22 August 2007 an announcement on the official Xbox website stated that Microsoft will retrofit for free all the Wireless Racing Wheels that were manufactured during 2006 and 2007. This is due to a component in the wheel chassis that in rare cases may
overheat and release smoke when the AC/DC power supply is used to power up the wheel.[4]

According to Microsoft the retrofit of the Xbox 360 Wireless Racing Wheel is only required on products with SKU numbers 9Z1-00001, 9Z1-00002, 9Z1-00003, 9Z1-00004, 9Z1-00009, 9Z1-00011, 9Z1-00012, 9Z1-00013, 9Z1-00017, 9Z1-00018 and Wheel part numbers X809211-001,
X809211-002, X809211-003, X809211-004, X809211-005.

The SKU number can be found on a label on the bottom side of the retail carton and the Wheel part numbers are found on a label on the bottom side of the dashboard assembly. Any SKU or Wheel not included in this list will not require the retrofit

You can buy a fully adjustable stand for the Xbox 360 racing wheel.

Details here
wheelstandpro.com/.../wheel-stand-pro-for-microsoft-wireless-racing-wheel-for-xbox-360

How about they start with a firmware update for their very own product, the Microsoft Wireless Racing Wheel?

xbox 360 wireless racing wheel with force feedback