I am trying to convert 18,000 Emirates Skywards miles to Heathrow Rewards to pay for parking.

I go to the Partners/Heathrow Rewards section on the Emirates website and click the "Convert now" button. This takes me to the "Spend Points" page at the Heathrow Rewards website which does not have any further instructions to convert the Skywards miles to Heathrow Rewards points.

I am clearly doing something wrong but I cannot work out what it is.

Any suggestions will be greatly appreciated.