Calling Method in another class

AppendTextBox1 is defined in my Form1 class. How can I call it from another class to append text to my TextBox1?

using System;

namespace Program
{
  class MyClass
  {
    public MyClass()
    {
      AppendTextBox1("Hello World from MyClass" + Environment.NewLine);
    }
  }
}

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using System;
using System.Windows.Forms;

namespace Program
{
  public partial class Form1 : Form
  {
    public Form1()
    {
      InitializeComponent();
    }

    // This delegate enables asynchronous calls for setting
    // the text property on the textBox1 control.
    delegate void AppendTextBox1Delegate(string text);


    /* Call this method to append text to textBox1 */
    public void AppendTextBox1(string text)
    {
      if (this.textBox1.InvokeRequired)
      {
        AppendTextBox1Delegate d = new AppendTextBox1Delegate(AppendTextBox1);
        this.textBox1.Invoke(d, new object[] { text });
      }
      else
      {
        this.textBox1.AppendText(text);
      }
    }


    private void button1_Click(object sender, EventArgs e)
    {
      AppendTextBox1("Hello World from button1_Click" + Environment.NewLine);
      MyClass m = new MyClass();   //test
    }
  }
}

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