You just need to access Facebook Business integrations, then try to either delete the Shopify app from your Facebook or just click on it and add the business manager needed plus the other assets (like the facebook page and instagram accounts you want to link with your new shopify account)
You can access it directly from this link, or just go to Settings & Privacy then search for Business Integrations.
if you had any problems, just let me know and I can help you fix it.
if all what you had was a problem of not having your account sychronized with Shopify then deleting the app and install it again with me the best option, but if your account was rejected because of a problem either on your store or your Facebook account then I will need more than that to help you.
So can you please share a screenshot so I can understand exactly what's the issue?