Can't access to my page without www (error: Warning: Cannot modify header….

Hello!

I changed my site address using this method (the seconde one)
<a href=”https://asknoypi.com/2015/08/03/wordpress-cannot-login-after-domain-url-change/
“>
And now, my site isn’t accessible without www. in the adress

error:

Warning: Cannot modify header information – headers already sent by (output started at /home/ar***/public_html/wp/wp-config.php:1) in /home/ar***/public_html/wp/wp-includes/pluggable.php on line 1196

I went through the forum and guess it’s a file to correct but can’t figure out which is the one