Access Request Settings across site collections in a tenant

How can I find and change the email entered into the Access Request Settings on all site collections and sub-sites in an entire tenant. We have a user who is still with the company but is in a different job position. He was a tenant admin and his email was included on hundreds of sites and sub-sites as the person who would grant access to sites. We now need to remove his email address from the field. I've found numerous articles for a single site collection or how to do it on 2013, 2010, and 2007 but no good source for SharePoint online. Any help would be appreciated. My skills with PowerShell are very minimal so the more complete the script is, the better.