How ti update I/O’s 12.5.4 iPhone 6 my mobile not showing any update

The iPhone 6 is not compatible with iOS 13 or higher.

It is already updated to its maximum.

You cannot update an iPhone 6 beyond 12.5.4. You would need a newer phone to get the newer operating system.

The iPhone 6 cannot be updated beyond iOS 12.5.4. It does not have the components necessary to run newer software.

At least we all agree!