How to Downgrade iOS 26 to 18

Hello everyone,

I recently accidentally upgraded my iPhone to the iOS 26 developer beta. After using it for a few days, I found that the system has many new features. Unfortunately, my device is relatively old and not suitable for the latest iOS26 system version. Now I still want to roll back to the official version of iOS 18 that I am familiar with.

I have been using iOS 26 for about two days, and there are still many things that I am not used to. Can anyone share a clear, step-by-step downgrade method to restore my device to iOS 18 without losing important data?

Thank you in advance for your guidance or recommended tools!