Hi Adnaan,
Refer below code sample.
C#
string hijriDate = "1445/1/19";
System.Globalization.CultureInfo cultureInfo = new System.Globalization.CultureInfo("ar-SA");
cultureInfo.DateTimeFormat.Calendar = new System.Globalization.HijriCalendar();
DateTime gregorianDate = Convert.ToDateTime(hijriDate, cultureInfo);
VB.Net
Dim hijriDate As String = "1445/1/19"
Dim cultureInfo As System.Globalization.CultureInfo = New System.Globalization.CultureInfo("ar-SA")
cultureInfo.DateTimeFormat.Calendar = New System.Globalization.HijriCalendar()
Dim gregorianDate As DateTime = Convert.ToDateTime(hijriDate, cultureInfo)