Pairing an Apple Watch to an iPhone
How can I update my iPhone software when it shows it’s updated but is not? I’m trying to pair a Apple Watch to my iPhone.
iPhone 6 Plus, iOS 12
If you are attempting to pair a new Apple Watch that has watchOS 6 on it, you will not be able to pair it to an iPhone 6 Plus. It requires an iPhone 6s or above. There is no way you can update the iPhone, watchOS 6.x requires a device running iOS 13 or above.