Datatable reset

When pageload the first time, it looks fine. The second time, it keeps adding "- test" to column_tmp. How can I reset my_table the second time it reload?
pageload

my_table is datatable


 

For Each column As DataColumn In my_table.Columns

                Dim column_tmp As String = column.ColumnName
                Dim RequestAs String = Get_data(Session("test"), column_tmp)

                If RequestIsNot Nothing Then
                    my_table.Columns(column_tmp).ColumnName = Request_columnname
                   
                Else
                 
                    my_table.Columns(column_tmp).ColumnName = column_tmp &  " - test"
                           
                End If
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