Hi there,
try adding this PHP Snippet to your site:
add_filter( 'generate_navigation_search_output', function() {
printf(
'<form method="get" class="search-form navigation-search" action="%1$s">
<label for="nav-search">Search:</label>
<input type="search" class="search-field" id="nav-search" value="%2$s" name="s" title="%3$s" />
<input type="hidden" name="post_type" value="product" />
</form>',
esc_url( home_url( '/' ) ),
esc_attr( get_search_query() ),
esc_attr_x( 'Search', 'label', 'generatepress' )
);
} );