So I take it you're connecting via DXB to somewhere else.

There's no puzzle really. At check in in PRG you should be handed the hotel voucher (you'd need to book that from experience). When you land in DXB head over to the chauffeur desk with your inbound boarding pass, they'll pull up your chauffeur drive request and update it if needed. You can also change the pick up time and location. I once changed both at T-4 hours by calling EK's local number.