Inbox shows 1 unread email, but I can't see it?

Since I can't see it, I can't delete it. Tried "select all" in hopes of deleting it, but it won't select it. It's preventing me from seeing my Yahoo inbox on my iphone.

First the inbox total located just to the right of INBOX in parentheses is the total of all the messages still in your inbox that have not been read… Hovering your pointer over INBOX will give you the total of all of your emails in the inbox including those that have not been read. That will only change when you delete a message. When they are all read and it still indicates… Usually (1)… RIGHT click on the curved arrow to the right of the number… You can bring up the curved arrow by hovering your pointer in the blank area to the right of INBOX… And then click on MARK ALL READ and it should disappear. When you LEFT click on the curved arrow it checks for new emails.