How do I reset an email password in IOS 12.0.1?

You can't "reset" your mail account password from within mail or it's settings, you can only "change" it. To reset the password you will have to visit your mail providers website and do it from there (or with there help). They should then send you a new password which you need to enter under mail's settings (that might be by post).

This discussion talks about "changing" passwords email password change

If you just want to change the mail password for some reason, again you need go to the appropriate section of your mail providers web page, you usually enter your current password then enter the desired new password, once done you go back to mail's settings and change the password to your new one.

Hope the above helps.

The same way you did in iOS 12.0 and earlier.