How update without wifi
how update I phone 6s plus without wifi
how update I phone 6s plus without wifi
Connect it to a Mac or PC computer and do the update
that way.
This link offers instructions on how to do what imobl suggests. I’ve copied the pertinent part below.
Update your iPhone or iPad - Apple Support
Use your computer to update your device manually. Learn how to update your device manually if you're using a Mac with macOS Catalina or later, or if you're using a Mac with macOS Mojave or earlier or a Windows PC.
How update without wifi