Create an account on myAudi.com
He will need the VIN number for the initial registration.
Once account is set up and logged in, go to Audi Connect—>Map Update.
You can select full European map set, or just UK, then download, follow instructions. I find it easier to transfer files to a usb stick, then pop in MMI usb slot.
You can now go to MMI navigation settings and update from there, selecting usb as the source.
Depending on your MMI version, you may have an option to download over your 4G connection, if you have a data SIM installed.
It’s quite a large file size, so I prefer to use broadband speeds, and not use up data allowance.
If your using a MAC instead of a PC, you need latest flash version installed and enabled before you start the download.