Garmin Nuvi67LM changing maps

[Kevaclone]

Been a few years since I have played with Garmin devices

So friend bought this Nuvi67LM
Wanted me to update the maps
Problem. He bought it used. No history but it looks new
I am assuming the original owner bought it online from the US maybe as it is loaded with US maps which is why he's sold it on very cheaply
Express wants to update US maps only

It appears the old method of just loading unlocked maps no longer works
I removed the US map and copied an unlocked 2018 Aust/NZ map into the "System" folder
Have reset the unit and started it. and went outside to get GPS fix.
But shows "maps can't be unlocked" msg after bootup
And express still wants to update with US maps(assuming there is a data file that tells express which maps it should have)
Reset via advanced menu(holding the speed indicator in the dash board) still nothing

Anyone enlighten me as to the workings of these new units please?