private void btnExportar_Click(object sender, EventArgs e)
        {
            formExportar form = new formExportar();
            form.ShowDialog();

            if (exportar.txtsenha.Text == "123")
            {
               //código para exportar arquivos para o excel
            }
            else
            {
                MetroFramework.MetroMessageBox.Show(this, "Senha incorreta", "Erro", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }
    }

public partial class TelaInicio : MetroFramework.Forms.MetroForm
    {
        internal formExportar exportar = new formExportar();

    public TelaInicio(formExportar exportar)
    {
        InitializeComponent();
        this.exportar = exportar;
    }