Error_Log Filling Up

I am getting loads and loads of this error message in my error_log file from this plugin. Is there some sort of fix? It is for the website Sweet Hollywood

04-Sep-2024 14:32:39 UTC] PHP Warning: session_start(): Cannot start session when headers already sent in /home/u1e2sz2cacmk/public_html/wp-content/plugins/custom-background-for-post-and-page/custombg.php on line 31

The page I need help with: [log in to see the link]