C# Win Form ส่งค่าที่ได้จาก subform คืนให้ main form ทำยังไงครับ

public partial class test1 : Form
    {
        public string data;

        public test1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            test2 frm = new test2();
            frm.ShowDialog();
        }
        public void setTextBox(string senddata){
            data = senddata;
            textBox1.Text = data;
        }
    }

public partial class test2 : Form
    {
        public test2()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            test1 frm = new test1();
            frm.setTextBox(textBox1.Text);
        }
    }