Is this a one time thing?
If so, you might be better off inserting it directly into your database (using MySQL Workbench, etc.) rather than trying to use the dataset to mess with dates.
You can then use SQL to delete/move unwanted data.
There are a few differnt sites that can help you with that import. http://www.mysqltutorial.org/import-csv-file-mysql-table/
However, if you will be regularly opening, modifying, and importing many csv files, your method is probably more appropriate.