Update Specific cells in existing Excel Sheet using C#

Hi

I am having a excel which is designed with the particular column and also with the design. I mean here is i have a excel with the fixed header and i need to write the content in the particular column of the excel.

for sample, i am having a excel with the column FirstName  and LastName. From the program, i need to write only firstname from the List of object or datatable to the excel and save it in another folder.

Hope this is clear, please let me know if this is not clear.

Thanks.