Hi Ale,
There is a nice tutorial showing how to search WordPress by all custom fields. It requires some coding and works for all text fields.
Or you can modify the query like this:
add_action( 'pre_get_posts', function( $query ) {
if ( is_admin() || ! $query->is_main_query() ) {
return;
}
$query->set( 'meta_query', [
'relation' => 'OR',
[
'key' => 'field_id1',
'value' => '"' . get_search_query() . '"',
'compare' => 'LIKE'
],
[
'key' => 'field_id2',
'value' => '"' . get_search_query() . '"',
'compare' => 'LIKE'
],
[
'key' => 'field_id2',
'value' => '"' . get_search_query() . '"',
'compare' => 'LIKE'
]
] );
} );