When you add your Instagram channel, you will be asked if you want to connect with Facebook. You can also enter the URL manually, if you don't have a business account.
Click on 'continue with Facebook' and log in with your Facebook business page. This page must also be linked to your Instagram business account. After you have logged in and you're connected successfully, you can enter the demographics of your followers. You have to d this manually. You can find the statistics in the Instagram app.
Check the article for more information about Instagram business.