Form1 had one button if we click that button it wil show another form(Form2)

Form2 currentActiveForm2 = null;
void yourButton_Click(object sender, EventArgs e)
{
    if (currentActiveForm2 != null)
    {
        currentActiveForm2.Close();
        // if currentActiveForm2 is null, your button has not been clicked yet, so the form doesn't exist yet and we cannot close it.
    }
    currentActiveForm2 = new Form2();
    currentActiveForm2.Show();
}