Cannot modify header information – headers already sent by

And this message appears on my index page : Notice: wp_deregister_script was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or init hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.) in [SERVER INFO]\wp-includes\functions.php on line 2959

and one more thing… paste the wp_deregister_script from your functions file as it’s hard to guess what’s there.
you’ll find it in functions.php on line 2959 and around

Try:
– switching to the default theme by renaming your current theme’s folder inside wp-content/themes and adding “-old” to the end of the folder name using FTP or whatever file management application your host provides.

– resetting the plugins folder by FTP or phpMyAdmin.

I tried to reset the plugins as you told me. => It doesn’t work
Tried to switch to default theme => doesn’t work
I can’t find the wp_deregister_script. => Not in wp-includes/functions.php

What is this CSS error message on my index now ?

How could I access to my wp-admin page please ?

Here is the code in pluggable.php at line 876

function status_header( $header ) {
	$text = get_status_header_desc( $header );

	if ( empty( $text ) )
		return false;

	$protocol = $_SERVER["SERVER_PROTOCOL"];
	if ( 'HTTP/1.1' != $protocol && 'HTTP/1.0' != $protocol )
		$protocol = 'HTTP/1.0';
	$status_header = "$protocol $header $text";
	if ( function_exists( 'apply_filters' ) )
		$status_header = apply_filters( 'status_header', $status_header, $header, $text, $protocol );

	return @header( $status_header, true, $header );
}

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No idea for anybody ?

The URL of my website is

https://www.nextdaysfilms.com