First, go to your store’s Facebook page. In your web address, (e.g. www.facebook.com/boutir.hk), your Facebook ID is the name or number after the slash, i.e. boutir.com. You may check your own Facebook ID via https://findmyfbid.com as well.
Your Instagram ID would be easier to find as it is in fact, your account name. As the example below shows, the Instagram ID is “boutir”.