test.cs

private void Form1_Load(object sender, EventArgs e)
{
    RibbonButton rbtnClickMe =
        new TXTextControl.Windows.Forms.Ribbon.RibbonButton();
    rbtnClickMe.Text = "Click Me";
    rbtnClickMe.SmallIcon = Image.FromFile("checkmark.png");
    rbtnClickMe.Click += RbtnClickMe_Click;

    SetQuickAccessToolbarStandardItems(new RibbonButton[] {
        rbtnClickMe });
}

private void RbtnClickMe_Click(object sender, EventArgs e)
{
    MessageBox.Show("Click Me");
}