Please help, error on my website :'(

Dear all, im very new to wordpress and i got this error.. any kind soul please help me.. really appreciate..

my website: bryangoh.com
if i enter the URL with “www”, eg. https://www.bryangoh.com, the following error message will appear:
Warning: Cannot modify header information – headers already sent by (output started at /home/content/b/r/y/bryangoh/html/index.php:2) in /home/content/b/r/y/bryangoh/html/wp-includes/pluggable.php on line 897