How to pass variable from one view to another in SwiftUI

If View2 is being used in View1 you could do something like this:

View1:

struct FirstView: View {
    @State var count = 0
    var body: some View {
        VStack{
            Text("\(self.count)")
            Button(action:
                {self.count = self.count-10})
            {
                Text("-")
            }
            SecondView(count: self.$count)
        }
    }
}

And View2:

struct SecondView: View {
    @Binding var count: Int
    var body: some View {
        Button(action: {self.count = 0}) {
            Text("Reset")
        }
    }
}

Edit

If they are completely different views and need single source of truth you could use an observableObject/EnvironmentVariables. The best way would be to add the environment variable to the ContentView where it's first defined in the SceneDelegate

ContentView().environmentObject(SourceOfTruth())

Here is SourceOfTruth:

class SourceOfTruth: ObservableObject{
    @Published var count = 0
}

Then you could use EnvironmentObjects to the other views: Here is ContentView:

struct ContentView: View {
    @EnvironmentObject var truth: SourceOfTruth
    var body: some View {
        VStack {
            FirstView()
            SecondView()
        }
    }
}

Here is FirstView:

struct FirstView: View {
    @EnvironmentObject var truth: SourceOfTruth
    var body: some View {
       VStack{
        Text("\(self.truth.count)")
           Button(action:
            {self.truth.count = self.truth.count-10})
           {
               Text("-")
           }
       }
    }
}

Here is SecondView:

struct SecondView: View {
    @EnvironmentObject var truth: SourceOfTruth
    var body: some View {
        Button(action: {self.truth.count = 0}) {
            Text("Reset")
        }
    }
}