To link your Instagram account to your brand's Facebook Page, you first need to be an admin of that Page on Facebook.
To link your Instagram account to a Facebook Page:
Android
  1. Go to your profile and tap  in the top right.
  2. Scroll down and tap Linked Accounts, then select Facebook.
  3. If you haven't already, enter your Facebook login information.
  4. By default, your Instagram account will link to your personal Facebook Timeline. To link to a Page instead, tap Facebook again and choose a Page that you manage below Share to.
iPhone or Windows Phone
  1. Go to your profile and tap  in the top right.
  2. Scroll down and tap Linked Accounts, then select Facebook.
  3. If you haven't already, enter your Facebook login information.
  4. By default, your Instagram account will link to your personal Facebook Timeline. To link to a Page instead, tap Facebook again, then tap Share to and choose a Page that you manage.