You can use Parameter in report
Or
Add a Text box in the header of the report.
Change the "Name" of the Text box to say "txtHead"
Now in your application write those code
Dim objText As CrystalDecisions.CrystalReports.Engine.TextObject
objText = rptReport.Section4.ReportObjects("txtHead")
objText.Text = ds2.tables(0).rows(0)("HEADER")
Note this code is in VB.Net. Please convert it in C# in your way