1) After logging in to the Business Manager account, begin by clicking on the tab at the top left corner of the screen and click on "Business Settings".Check the left hand side of the screen and click on "Instagram Accounts", then click "Add New Instagram Account" at the center of the screen, as shown below:

Follow the directions to claim the appropriate Instagram account.

2) The product feed can now be added to the product feed in the Facebook catalog.  To create your catalog , follow the link: Create a Product Catalog