Hi Elizabeth,
Once an email is sent out by Marketo, it is downloaded by the receiving email client. At this point, Marketo has no way of changing those links.
If the erroneous link is on your Marketo Landing Page CNAME, you may be able to create a redirect rule to redirect users who go to the bad link as per this article: https://community.marketo.com/MarketoArticle?id=kA050000000LBHLCA4
Best,
Will