01) First step is to import the products to the facebook catalog according to this tutorial:

https://faq.mformula.net/content/23/1306/en-us/how-to-generate-and-import-the-product-feed-for-facebook-products-catalog.html

02) Step two is to change your Instagram to Business as per instructions:

https://business.instagram.com/a/shopping-setup-guide

03) Now just post and add the tag of your product on your Instagram