You have to customize the store.php file. In the plugin file you will get this file. If you want to create own custom store page then you have to customize the template. Huge customization will require.
I am not clear what are you looking for. Store page is already available in Dokan and it will appear with any WooCommerce compatible theme. Now if you want to create any custom template for the store page then you have to customize the store.php file. If you need to change the layout or anything on the store page.
If you want to make any CSS changes then you can do that by child theme style.css file. But if you want to change any templating then you have to override the template file which I have mentioned in my previous post.