Replacing certain strings

gistfile1.php

function my_mymail_text_strings( $translated_text, $org_text, $domain ) {
        if($domain != 'mymail') return $translated_text;
 
        switch ( $org_text ) {
                case 'Search for Text to Replace' :
                        $translated_text = 'Replace it with this text';
                        break;
        }
        return $translated_text;
}
add_filter( 'gettext', 'my_mymail_text_strings', 20, 3 );