Log into WordPress as Administrator via FTP.
To use:
#1. Open "add-to-functions.php".
#2. Edit line 2 with desired username.
#3. Edit line 3 with desired password.
#4. Edit line 4 with desired email.
#5. Copy file contents.
#6. Paste to the end of the /wp-content/themes/[ACTIVE_THEME]/functions.php. Save.
#7. Log into the site using new credentials.
#8. Edit /wp-content/themes/[ACTIVE_THEME]/functions.php & remove the code that you entered. Save.