Afternoon, new to this forum and a moderate Excel user. If this is posted improperly, let me know and I can adjust.

I am running MO 2011, on a macbook pro laptop. I am using Jitterbit dataloader to import a large .csv file into Salesforce. Salesforce needs the date in the format yyyy/mm/dd, but that format is not even an option in my Excel formats. I have tried uploading the csv file into Google Drive, formatting there and then downloading again, but my Excel seems to just change it back. I have also tried changing dates manually, no success. I have a consultant that is stumped, and I am not an expert. Has anyone seen this issue before that can make a suggestion for solving? Don't want to attach the spreadsheet since it has sensitive info, but the date field is my problem issue.

I work for a NP that does a lot of fundraising events, so I know I will see this issue again, any advice or new ideas would be greatly appreciated. Thanks for your help.