Navigation Stack Management

Code Block struct Testing: View {
    @EnvironmentObject var navHelp : NavigationHelper
    var body: some View {
        NavigationView {
            VStack {
							NavigationLink(destination:testing2(),
							tag : "testing2", 
							selection : $navHelp.selection) 
								{ Text("Go to two") }
            }
            .navigationBarTitle("Navigation")
        }
    }
}
struct testing2 : View {
    @EnvironmentObject var navHelp : NavigationHelper
    
    var body: some View{
        VStack {
            NavigationLink(destination:testing3(), 
						tag : "testing3", 
						selection : $navHelp.selection) 
							{ Text("Go to 2n3") }
        }
        .navigationBarTitle("Second Page")
    }
}
struct testing3 : View {
    @EnvironmentObject var navHelp: NavigationHelper
    var body: some View{
        VStack {
            Button(action: {
                    navHelp.selection = "testing2"
            }, label: {
                Text("Go to two")
            })
        }
        .navigationBarTitle("Third Page")
    }
}
class NavigationHelper: ObservableObject {
    @Published var selection: String? = nil
}

Code Block
struct Testing: View {

@EnvironmentObject var navHelp : NavigationHelper

var body: some View {

NavigationView {

VStack {
NavigationLink(destination:testing2(),
tag : "testing2",
selection : $navHelp.selection)
{ Text("Go to two") }

}
.navigationBarTitle("Navigation")
}
}
}



struct testing2 : View {

@EnvironmentObject var navHelp : NavigationHelper



var body: some View{

VStack {
NavigationLink(destination:testing3(),
tag : "testing3",
selection : $navHelp.selection)
{ Text("Go to 2n3") }

}
.navigationBarTitle("Second Page")
}
}



struct testing3 : View {

@EnvironmentObject var navHelp: NavigationHelper

var body: some View{

VStack {
Button(action: {
navHelp.selection = "testing2"
}, label: {
Text("Go to two")
})
}
.navigationBarTitle("Third Page")
}
}

class NavigationHelper: ObservableObject {
@Published var selection: String? = nil
}

I am trying to navigate to any page inside of my NavigationView. I made an ObservableObject and passed it in as an EnvironmentObject. I found a similar answer on stack about this.

I can get it to work to returning to the first page by setting the value to nil or the second page by setting the selection to testing2.

How do I get it to work with another layer? When I add a new tagged NavigationLink the NavigationView automatically goes back to the top of the stack.