How to update my iPhone 6plus

Very smart, so now you realise the iPhone 6 Plus is at the end of its days, it has been out since 2014, and cannot be updated to iOS 13, it will be stuck on iOS 12.4.7 permanently, but if you want to get iOS 13, you can get another iPhone, that is not on your 6+, maybe the iPhone S a second gen would be perfect for you, cheers

I'm happy you solved your problem. I guess you discovered that the iPhone 6 Plus can only be updated to iOS 12.4.7 and cannot run iOS 13.x. Good work.