Do a GEDCOM export from the laptop. then do a GEDCOM import on the desktop to import the new data and merge it into your main database. The Backup-Restore route is for "Restoring" your data after a crash.It will not "merge" with data already in a database.
Try not to export more to the GEDCOM than you need or you will have to merge a lot of individuals. That is, you will have two listings of all the old entrants that you will have to merge (combine) into one.