Your question will be impossible to answer until you show us the code you are already working with. I assume the source is an Excel worksheet, how do you open and read it? Through OleDb or the Excel PIA? Through OleDb and ADO, you would just query the data source properly. Through the PIA personally I would put the data in an easier worked container like a datatable and do approximately the same, through Linq.
Again, this question is like asking "How do I fit these two pieces together?" without us knowing what the pieces are or what shape they are.
It is really important when posting on a public technical forum to properly articulate what you are asking, and take the time to make sure the language used is appropriate, otherwise you force other people to work hard at just understanding your question, and considerably reduce your odds of getting a helpful answer...