new iphone6 has existing email account name incorrect and cannot sind in

Updated to iphone6 and cannot sign in to my existing yahoo email account on new phone because "email address you entered does not match your account" Problem is that name is the same, however, iphone has entered an uppercase letter instead of a lowercase letter. Do not want to delete account on phone and set up old one because need access to some of the emails on the server

help or advice?