woocommerce

every time I try to add a product to my cart this message comes up

Warning: Cannot modify header information – headers already sent by (output started at /home3/chomg/public_html/wp-content/themes/customizr/inc/parts/class-header-nav_walker.php:74) in /home3/chomg/public_html/wp-includes/pluggable.php on line 1121

please help I am not very good with coding so please be very specific

https://wordpress.org/plugins/woocommerce/