Upgraded my Galaxy S9+ from Oreo to Pie and wish I didn't. Some major issues such especially with Bluetooth. If anybody upgraded only to downgrade back to Oreo let me know how you went about. I seriously find Pie horrible.
I am sorry to hear that you're experiencing such issues with the new update. I'm always concerned about updates and tend to delay installing them until I've checked to see what potential issues might come with the update.
From what I understand, you would need to root your device in order to roll back an OS update on your Android device, which we can't offer support with here. There is no officially supported way of rolling back an update unless the manufacturer issues a rollback themselves.
Rooting is not without risks so I can't recommend it. If you're having Bluetooth related issues, I would recommend checking to see if the Bluetooth enabled devices have firmware updates available. I know this doesn't apply to all Bluetooth enabled devices but it's worth a shot!
One thing to be aware of is some video apps from the certain tv networks and BDUs will refuse to play on rooted devices and its well within their rights. If you are okay with this major inconvenience then sure go ahead otherwise try not to mess with the phones and just focus on using them how the manufacturers had intended it