请看下面的链接：

如何追加现有的使用C＃的excel文件？ [ ^ ]

如何在C＃中打开Excel文件 [ ^ ]

如何将值附加到Excel文件？ [ ^ ]

Please have a look on the bellow link :
How to append existing excel file using C# ?[^]
How to open an Excel file in C#[^]
How to append values to an Excel file?[^]