Attributes are saved as Product attributes instead of Global Attributes

Hello
I have used CSV method to import thousand product from shopify to woocommerce.
The products were imported with images without any issue. But the attributes have become as custom product attributes instead of Global attributes. Now the problem is these custom attributes are not available on front end in filter by attributes widget.
Is there a way to convert this custom product attributes into global attributes or display these custom product attributes in Sidebar to be able to filter product on category page and shop page.