How do I transfer BlueChart G3 charts to a new device?

I bought the HXEU001R - English Channel charts earlier this year and was using them on my eTrex 30x. I've now bought a GPSMAP 66i and I want to transfer them onto the new device.

I can't see any way to do this in Express. How can I transfer them (just putting the microSD card in the new unit didn't work, but I didn't expect it to).