Feels like you have asked this question before.
string cmd = String.Format("SELECT * from mobilesubscriberdata1 where m_date='{0}'", dateTimePicker1.Value.ToString("yyyy-MM-dd"));
dt = obj.GetDataTable(cmd);
Make sure the date format "yyyy-MM-dd" matches the expected date format of your database.
You also need to consider the locale used by the database, if you have databases in different parts of the world.
Custom Date and Time Format Strings[
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