Query a datatable and make the value null

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C#

I have a datatable and i am getting 2 rows like Recommendations and priority and whenever Contact Specialist text is there i want to make it null

if (_dtrecomendationData.Select("Priority = 3").Length > 0)
                   {
                       DataRow[] dr = _dtrecomendationData.Select("Recommendations = Contact Vibration Specialist");

                       foreach (DataRow dre in dr)
                       {
                           dre["Recommendations"] = "--";
                       }

But i am getting an error like [System.Data.SyntaxErrorException] = {"Syntax error: Missing operand after 'Vibration' operator."}