App should import variants properly, so if they were not imported most probably you've just missed that checkbox in the import settings (it's optional feature).
In that case you may send our support team a file you were importing so we may check it on our side and make sure it's parsed properly with our app. Also you may grant us an access to your Store Admin and we'll re-import it for you free of charge (incl. variants) and make sure all the products were imported properly. Please send invitation to support@nexusmedia-ua.com and let us know once done.