PHP Warning: Cannot modify header information – headers already sent in

Hi
We are facing an error code happence in error_log file:
…………………………………………………………………………..
[21-Nov-2022 14:27:21 UTC] PHP Warning: Cannot modify header information – headers already sent in /home/myshopsh/public_html/wp-content/advanced-headers.php on line 12
[21-Nov-2022 14:27:21 UTC] PHP Warning: Cannot modify header information – headers already sent in /home/myshopsh/public_html/wp-content/advanced-headers.php on line 13
[21-Nov-2022 14:27:21 UTC] PHP Warning: Cannot modify header information – headers already sent in /home/myshopsh/public_html/wp-content/advanced-headers.php on line 14
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After opening the advanced-headers.php file under /wp-content we found those lines:
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<?php
/**
* This file is created by Really Simple SSL
*/

defined('ABSPATH') or die();

if ( isset($_GET["rsssl_header_test"]) && (int) $_GET["rsssl_header_test"] ===  211414390 ) return;

//RULES START

if ( !headers_sent() ) {
header("X-XSS-Protection: 0");
header("X-Content-Type-Options: nosniff");
header("Referrer-Policy: strict-origin-when-cross-origin");
}

……………………………………………………………………….
Like you see this PHP content file is created by Really Simple SSL.
Now, How to fix and prevent those headers and get rid of those errors?

Thanks

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