I loose mine every so often and have to go find it. It's a Widget and not an app.
On that first screen where it would normally be, put your finger there with a little pressure and hold it. You should then see some of the widgets come up and the weather should be one of them. Put your finger on the weather widget and slide it to the first screen.
It that doesn't work, go by any cell store and they should be able to help you in a few seconds.
Bill
Nodwell RN110 out moose hunting. 4-53 Detroit, Clark 5 spd, 40" wide tracks, 10:00x20 tires, 16,000# capacity, 22,000# weight. You know the mud is getting deep when it's coming in the doors.