Where did you buy the update? How do you know Express doesn't recognise the sd card? See also if this FAQ helps, including the 'related content' links at the bottom.
Update purchased from Garmin. At the bottom of the info popup on Garmin Express, the green line says 1.9gb used, but the card is 32gb. There is no option listed to install to the sd. Now when I log into my account to re-activate the update on the website, a window pops up to state there is trouble with the server. I have formatted the sd disk on windows 10.