OK, if you've got an older Ubisoft version, you'll most likely have to go the wonderful Ubisoft tech support route. That's what I had to do. Be prepared for much frustration and repition of yourself and the issues in multiple postings... I'm trying to remember what all I had to go through. Do you happen to remember your "account" information with them? You definitely have to start a "ticket" at
https://support.ubi.com/en-US and toward the bottom of the page is "Sign in to start a support case". The old installer no longer works, and they will have to send you a link for a new version of it. The new version will only be good for a limited amount of time... like two weeks, so be ready to install it...