How do set default value for navigation list for a list view on split screen?

I have a screen with a list that one side is empty when use on a iPad. as seen in the image or mac is empty .

The code below

import SwiftUI


// How to declare an array
var stockalertdtas :[StockAlertDta] = [testStockAlertData,testStockAlertData]

struct StockAlertListUIView: View {
  @StateObject var viewModel = StockAlertListUIViewModel()
  @Environment(\.horizontalSizeClass) var horizontalSizeClass
  @State var firstSelection: StockAlertDta?
   
  var body: some View {
    NavigationView{
      ZStack{
        //how to select the first value in the f
        List() {
        ForEach(viewModel.userStockAlertDtas, id:\.self){
          stockalert in
          NavigationLink(destination: StockDetailUIView(stockAlert: stockalert), tag: stockalert, selection: self.$firstSelection) {
              
              StockAlertRow(stockAlertDta: stockalert)
            }
        }.onDelete(perform: { IndexSet in
         
          IndexSet.forEach{ array_id in
            viewModel.deleteItem(atOffsets: array_id)
          }
           
           viewModel.userStockAlertDtas.remove(atOffsets: IndexSet)
           
        })
      }
        if viewModel.userStockAlertDtas.isEmpty {
          EmptyState(imageName: "empty-order", message: "You have not created any Alerts\nPlease create some alerts")
        }
         
      }.navigationTitle("Alerts")
    }.onAppear{
      viewModel.getAllStockAlert()
      let stockAlertHelper = StockAlertHelper()
      stockAlertHelper.hasTargetsBeenReach()
      viewModel.getInstruments()
       
      if self.horizontalSizeClass == .regular {
        self.firstSelection = viewModel.userStockAlertDtas.first
        }
      }
    }
}

struct StockAlertListUIView_Previews: PreviewProvider {
  static var previews: some View {
    StockAlertListUIView()
  }
}

How do i solve this issue?