The first thing that you could try is using the key lookup tool that the developers provide at this address: https://www.dvdvideosoft.com/tools/restore-subscription-key.aspx . It's specifically designed for dealing with this kind of situation. All you have to do is to enter your email address and if you have any keys attached to that account, they will be automatically resent into your inbox.
In case that doesn't help, your best bet would be to contact the manufacturer's Help Desk directly and ask them for assistance.
As far as the download link is concerned, simply go to the DVDVideoSoft download page and select the desired product.