1. Add from the Instagram App:

Open the Instagram app → Select 'Edit Profile → Under Public Business Information, Select Page → Choose a Page from your Pages that you'd like to connect to or select 'Create a New Facebook Page' → Done.

2. Add from the Facebook website or App:

On the sidebar, under Explore, click Pages > Click the name of the Facebook Page you want to work with > Settings > Instagram >  Log in to your Instagram account > Enter your user name and password and click Log In.

3. Exit the app from the background mode and reopen it again. Open the left menu → Click Profile to ensure that your Instagram account has been added.