URL CANONIQUE

hello, i change my home page and i try to index it on search console but this message appears : “Page en double : l’URL envoyée n’a pas été sélectionnée comme URL canonique”; i try to add a canonique URL but i can’t find it on dashboard of my wordpress (rankmath/title & meta) also i try to add the code on my page function.php , please any help.

N.B: this is the code i add on my function.php page :

add_filter( ‘rank_math/frontend/canonical’, function( $canonical ) {
$custom_url = RankMath\Post::get_meta( ‘canonical_url’, get_the_ID() );
if ( $custom_url ) {
$canonical = rtrim($custom_url,”/”);
}

return $canonical;
});

thank you