Date and Time won’t let me turn off Set Automatically

I was going to change the date on my phone as a funny prank on my sister, I was going to make her think it was Monday and not Sunday, I knew how to do this on my old phone, so I went to general, then I went to date and time, and finally I went to turn off set automatically. But, the switch wouldn’t turn off, it was frozen in the on position, it was also stuck in the time zone. Please help, the time zone is right, but I want to turn off set automatically.