How can I put navigation into an existing program?

struct viewdetail: View { @State var text1:String = "" @State var tip1:String = "" @State var text23:String = "" @State var tip23:String = "" var body: some View { Text(text1);Text(tip1);Text(text23);Text(tip23) } } func detailline(costa:inout [Double],tipa:inout [Double]) { print(costa,tipa) text1 = "125" Cannot find 'text1' in scope print("detail") }