I need info on how to change my IMAP password

It is a GMAIL account and I changed in in Google but I cannot receive email. I changed the SMTP password with no problem but not the incoming mail password. I cannot find where to change this.

I looked in Keychain but it presented me with dozens of options when I typed in my email address to search for where to change the password.

That would depend on who your email service provider is. Usually, you would go to their website and log in. Generally, you'll see a "Forgot Password" button of some sort on the log-in page.

Delete your Gmail account from your phone and add it back. That will update all the settings.