The import button only work with HH file. It will not work with the DB zip file.
If you are playing on a site that provide hand history, I suggest copying the files from the processed folder(location found in DH site settings) then import it on your other PC.
If you are playing on a site that does not provide hand history, go to overall report, right click the hand# then export hands for 3rd party. Import the exported hands to your other PC.