SwiftUI: How do I tell when my device orientation changes

Sorry to repeat this, but the new style forum won't allow me access to the original version of this question, and the answers.

I have been searching the internet for 3 or 4 days now to find only complex solutions that I cannot get working.

All I want to do is determine when the device orientation changes so that I can update the background Image. This is what I have so far:

Import SwiftUI

struct Main_Menu_iPhone: View {
    @State private var bloodGlucose: Float = 0.0
    var body: some View {
        ZStack {
            Image("iPhone Background Portrait 828 x 1792 ")
                .resizable()
                .aspectRatio(contentMode: .fill)

           VStack {
               HStack  {
                   Label("Blood Glucose", systemImage: "drop.fill")
                   TextField("Blood Glucose : ", value: $bloodGlucose, format: .number)
                       .onSubmit() {
                           print("Your Blood Gluse is : \(bloodGlucose)")
                       }
                       .background(.white)
                       .frame(alignment: .topTrailing)
                        Spacer()
               }
                     Spacer()
           }.padding(.top, 250)
        }
        
    }
    
}