Modifying parameter in CR during runtime

I have a report that opens up with all records showing. I would like to add filter using a text box that would narrow the report down to just one record. I have tried this a couple of different ways but I have not been able to find one that works

VB Code:

Dim report As wageChange
        Try
            report.DataDefinition.FormulaFields _
                ("?Employee").Text = txtNewEmpNumb.Text
            report.Refresh()
        Catch ex As Exception
            MsgBox("There is a problem with the report" & vbNewLine & _
            "Error: " & ex.Message & vbNewLine & _
            "Trace: " & ex.StackTrace, MsgBoxStyle.OKOnly, "Report Error")
        End Try
    End Sub

The error I get is object reference is not set to the instance of an object.