I deleted the gmapprom.img and gmapprom.sum and copied in the downloaded gmapprom.img.
I then replaced the largest db in the SQlite folder with the downoladed file D3413200A db.
BTW. The link in this forum for that file shows as "File has been removed due to copyright issues".
On this page : new-maps-f88/city-navigator-europe-ntu-2017-t18606.html
The "UK & RoI: Image UnLocked" file I downloaded has three different JCV folders
but the garmin only has one JCV folder just called "JCV".
I copied in the jcv file from the laneassist folder because it had a similar file name.
Is that the correct file to replace and if so how can I test if it works?
The map seems to work fine and it has my sisters street on it which is a new street.