I made a mistake setting up my Comcast email and now I don't know how to delete the bad account. I have both comcast.com and comcast.net but only the .net is valid.
Go to the phone settings and look for the Accounts listing. You should be able to remove the bad account from there. I don't have the exact steps as I don't have the S5. My steps should be similar though and are Settings > Accounts > select the type of account> select the email address you want to delete > menu button > remove account
How to delete an email account from my Samsung Galaxy S5
