Phone icon shows 4,232 emails, but the emails are gone

I have an iPhone 8 with IOS 12.3.1. Recently I tried to clear all of the messages from one of my email accounts. It seems there were thousands. I must have done something wrong as I may have flagged them or marked them unread or something. Now, my phone icon shows 4,232 emails for that particular account, but the emails are gone. They are not in Junk or Trash or read or unread. They are not there - which is a good thing, but the icon and the actual email account shows them as there.

How can I clear the icon and mailbox to ZERO, which would reflect the fact that I do not think they are there?

[Re-Titled by Host]