Of course, it's all there.
If you scroll down the main page, on the last blue ribbon you will find a field "Contact us"
(
https://www.mobileread.com/forums/sendmessage.php)
where you can submit your issue.
Or you use the list "View Forum Leaders"
(
https://www.mobileread.com/forums/showgroups.php)
and pick one of the moderators to send him a private message. Of course, it makes most sense to contact one of the "Administrators".