1. Go to the settings page of your facebook account.
https://www.facebook.com/settings/?tab=profile

2. Enter the Accounts Center.

3. Click the add accounts


4. After successfully adding the account, the account center page will display two connected accounts.

5. At this point, when posting on Facebook, the Instagram option will already be displayed.

6. Agree to share your facebook post and stories to the Instagram profile.

Click on the link to view Chinese version:
https://veryfb.com/d/890-ru-he-jiang-facebookde-tie-zi-fen-xiang-dao-instagram