How to change email verification sign in

Hi there !!! Im setting up a new iphone for my Wife. im doing it manually, bypassing all the secure log ins. when i waspromp to put in a email address, i used a old gmail account. This Gmail address is to access Apple Apps. i cant get in no matter what I try. I never used Gmail i been using Yahoo. How do i remove Gmai Login an enter a Yahoo signin ??? ( wHEN YOU SET UP THE PHONE THEY GIIVE YOU A NUMBER OF EMAIL ACCOUNTS TO CHOOS FROM. oNE TIME ONLY.) I hope i am making my self clear ??? I been work on this for many days . HELP !!!! PLEASE !!!

Thank you !!!! What keeps happening, is the Gmail Account i am trying to eliminate is the problem ??? To follow the prompts to make changes i am directed to verify my Gmail address ( The 1 used to set up the IPhone, GMail ,i dont have a password ,the Account was set up years ago. I never used it , in setting up the phone manually , remember im bypassing touch ID, and Icloud. The phone is for my wife ,we are old and dont want all the Bells And Whistles . Phone, Text,GPS,(Got it.) Question, why did i use a Gmail address to setup the phone ????? AH ME. one thing, whatever you try to change or add ,you are always asked to verify your email address ???? Cant do it ????