How do I rename all listbox items in VBNET

void Main()
{
	MyForm mf = new MyForm();
	//mf.ShowDialog();


}

public class MyForm: Form
{
	public MyForm()
	{
		this.Size = new Size(600, 340);
		this.Text = "MyForm";
		InitializeControls();
		this.Show();
	}
	
	private void InitializeControls()
	{
		//ListBox1
		ListBox1 = new ListBox(){Location = new Point(10,10), Size = new Size(150, 280), Anchor = (AnchorStyles.Left | AnchorStyles.Top | AnchorStyles.Bottom)};
		for(int i =1; i<=20; i++)
			ListBox1.Items.Add($"Item_{i}");
		
		//Button1
		Button1 = new Button(){Location = new Point(180,10), Size = new Size(120, 24), Anchor = (AnchorStyles.Left | AnchorStyles.Top), Text = "Change text!"};
		Button1.Click += Button1_Click;
		
		//add controls
		this.Controls.Add(ListBox1);
		this.Controls.Add(Button1);
	}

	private void Button1_Click(object sender, EventArgs e)
	{
		Button btn = sender as Button;
		string btnText = btn.Text == "Change text!" ? "Change again ;)" : "Change text!";
		char splitOn = btn.Text == "Change text!" ? '_' : '@';
		string replacement = btn.Text == "Change text!" ? "@" : "_";
		
		for(int i=0; i<ListBox1.Items.Count; i++)
		{
			object item = ListBox1.Items[i];
			string[] parts = item.ToString().Split(splitOn);
			string newText = parts[0] + replacement + parts[1];
			ListBox1.Items[i] = newText;
			btn.Text = btnText;
		}
	}
	
	
	private ListBox ListBox1;
	private Button Button1;
	
}