I too think Humble Bundle is the right place to ask for this.
https://support.humblebundle.com/hc/en-us/articles/211713188-Changing-Your-Registered-Email-AddressI found this page, where the change of the mail is described when you have an account there.
At the bottom of the page is a link for contact the support - that might also be the right place to ask, even if you have no account there but have issues with the mail address.