Save Multiple data in a local file in my computer at once.

if you want to store locally means xml / csv / Json / Excel file or local sql database. Refer below article to store datagridview data to CSV local file.

 

https://www.c-sharpcorner.com/blogs/export-datagridview-data-to-csv-in-c-sharp#:~:text=Export%20DataGridView%20Data%20To%20CSV%20In%20C%23.%201,sqlQuery%20%3D%20%22SELECT%20%2A%20FROM%20tblEmployee%22%20%3B%20

 

https://www.c-sharpcorner.com/blogs/export-datagridview-data-to-csv-in-c-sharp