Follow few instrcution to Setup Email Account on iPhone:
- Go to "Home" Screen, tap the "Settings" icon option.
- Now Tap "Mail, Contacts, Calendars".
- After that Select the Account which you want to modify.
- Tap "SMTP" under "Outgoing Mail Server".
- Now tap the Primary Server.
- At last enter your new password in the "Password" field.
Still getting issue then i suggest you to follow iPhone Error 1671 blog to gathered more details.