Hello, The problem of lowering IOS 13.0 down to IOS 12.0

MacOSX and iOS
1

I use the Iphone 7 plus, I missed the upgrade to IOS version 13.0, but I found the use is no longer smooth, so I decided to downgrade to IOS version 12.0, but I failed to downgrade, I have to how. Should I continue to downgrade IOS 12.0?