First let's make sure you have an alternate login option added to your JioSaavn account before the Facebook account can be unlinked. You can check this in JioSaavn App Settings > Edit Profile. If you do not have any other credentials apart from your Facebook account, please enter an email ID or mobile number, and tap Save.
Once you have an alternative login option, please write to us from the JioSaavn App Settings using the 'Contact us/Chat with us' option to get your Facebook account unlinked.