Find Index of a Column that Contains a Value in a Row

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C#

SQL

ADO.NET

I have a datatable that was imported from excel. Because of how it gets imported I need to Name the Columns based on the entries on the first row.

foreach (DataColumn c in spreadsheet.WorkbookData.Tables[0].Columns)
            {

                string cellValue = spreadsheet.WorkbookData.Tables[0].Rows[0][c].ToString();
                spreadsheet.WorkbookData.Tables[0].Columns[c.ToString()].ColumnName = cellValue;
            }

This works great, but when it hits a certain point the column names would start repeating. I want to make it so I just do a "m_" + cellValue when I come to where it starts repeating. I know where it starts repeating(I can open the excel file), but I want to be able to find that point based on a search(in this case at the second occurrence of "EDI_Std_Nomenclature") so the user could update the table if it ever changed.