There is a way that doesn't involve nginx regex's (https://xkcd.com/208/)
If you are comfortable accessing your civicrm database directly you can locate the correct row in the civicrm_mailing_trackable_url and update the value of the url.
If you run
select id, url, mailing_id from civicrm_mailing_trackable_url where mailing_id = X;
Where X is the ...
It sounds like you have "http://" hard-coded into your URLs. Check your BASE_URL in civicrm.settings.php (and search the whole file for "http://" while you're there), and check the Administer » System Settings » Resource URLs menu to ensure that your resource URL doesn't include "http://".
Finally, check if you have any extensions that have the text ...