private void SettingsDLT_delete_button_Click(object sender, EventArgs e)
{
    MainWeight main = new MainWeight();
    main.RemoveAllWeight();
}

public void RemoveAllWeight()
{
    try
    {
        using (DaghanKantarEntities context = new DaghanKantarEntities())
        {
            context.tbl_MainWeight.RemoveRange(
                context.tbl_MainWeight.Where(c => c.fldId != null));
            context.SaveChanges();
        }
    }
    catch (Exception exp)
    {
        throw new Exception("Hata: Kayıt Silinemedi - " + exp.Message.ToString(), exp);
    }
}

DBCC CHECKIDENT ('table_name', RESEED, 1)