How do I update my iPhone to iOS 13.4?
How do I update iOS 13.4
[Re-Titled by Moderator]
iPhone 6s Plus, iOS 12
If your phone is indeed the 6S plus, you can update to iOS 15.6.
But I am afraid that you're talking about the iPhone 6 Plus without the S. That model iPhone cannot be upgraded past iOS 12.5.5 due to hardware restrictions