Not really sure I follow. I tried both 'Red Hangup' + '*' + 3 and 'Red Hangup' + '#' + 3 and neither of them worked.
'Red Hangup' + '*' + '3', initially brought a message, reading from USB drive, and then it obviously said failed. so I suspect this is the right combination, however, I need some sort of USB drive to load it.
I'm not desperate to find the HMI, I will take it to the dealer in February and see if I can get Android Auto. Otherwise, there's a a company near Heathrow that can do this for a charge. They work with Mercedes and they said to me that having checked my VIN that it is possible to add Android Auto. I'm using this option as my last resort after Mercedes tells me it's not possible.