Downgrade iPad Mini 2 to iOS 10.3

When iOS 11 was released I had to downgrade back to iOS 10.3 due to poor performance on my iPad mini 2. After continually being annoyed by reminder messages for months to upgrade my device and told that iOS 11.3 had solved the performance issues with the A7 devices, I was disappointed after the upgrade to 11.3 to still be dealing with jumpy graphic transitions, poor responsiveness and random freezing. The problems only occur in iOS and apps such as Safari. All my other apps run well.

This seems to be a common issue for other owners of the iPad mini 2. I want to downgrade back to iOS 10.3.3. Where can I register my device so I can have an older iOS image signed by apple or whatever I need to do in order to downgrade my device?