Hello @HeatherT383 ,
If you have advanced permissions turned on in your Settings, for mass-changing permissions I'd recommend uploading a CSV / XLS file with all those email addresses that need changing. On the page where you mark that you understand permissions and select a permission type, select the one you want and continue to uploading. You can just upload this file to a separate list (won't affect their other list memberships), and then Delete the List Only.
Additionally, once advanced permissions are turned on, you can mass unsubscribe people by uploading a file of email addresses.
Have you tried deleting the contacts out of the system (exporting and downloading them first), then reuploaded them to applicable lists, @HeatherT383? Beyond that, you may need to speak with our Review team to see if they have any additional insight to get these contacts switched to express permission en masse.
really...deleting that many contacts and then reloading. should be easy switch just as it was to take them off the express permission.