You should be able to change by going to tools/options/system options/locations and scrolling to get to the "templates" section.
I'm assuming your client is going to Tools - Options -System Options - File Locations - document templates? When doing that, there should be a Browse button to insert the new location. Then, when starting a new document, the templates in this location should be available (assuming that the "Advanced" button has been selected in the new document dialog box and not the "Novice" one). At what point in that process is the problem occurring?
Select your "File Locations", restart SW. Then, go back and select your Default Templates.
Sometimes it gets a little picky.