Resynchronizing? Keyless start fob for MK2 2014

[Deegs]

We just bought our first Galaxy- whoop! A TDci 2.0 14plate. 

But. Alas. As the fob key battery warning kept appearing we changed the battery, a standard 2032 3v, in the keyless start fob. 

But now verily the car remaineth alarmed and locked on the drive. When we try and use the key nothing happens. Tried letting myself in using the metal key piece from inside. But the car sayeth, I know thee not, away from me, evil-doer. 

So how do I reprogramme or resynchronize a keyless fob for a MK2? 

Any help gratefully received.