Navigate to the Module that contains the Date Format you are using for the Date Output, insert a Line Item "Format Date" and populate the Formula referencing the Line Item with the Date, but format the line item as TEXT. Once you have your date format, the Formula should be as such:
TEXT(YEAR(Format Date)) & "-" & (IF LENGTH(TEXT(MONTH(Format Date))) < 2 THEN "0" & TEXT(MONTH(Format Date)) ELSE TEXT(MONTH(Format Date))) & "-" & IF LENGTH(TEXT(DAY(Format Date))) < 2 THEN "0" & TEXT(DAY(Format Date)) ELSE TEXT(DAY(Format Date))
This will give a date output of YYYY-MM-DD but you can switch around the logic to obtain MM-DD-YYYY or replace the "-" with "/" if you want that format.
While you can do that, it is best practice that you don't and instead break that up into multiple line items so it is cleaner, easier to read/maintain, as well as it performs better because the formula is no longer single threaded. So, you would have four line items: one for Year, one for Month, one for Day, and the last one which puts them all together.
What is even simpler is to use a defined format of YYYYMMDD and specify that in the import
No need for any manipulation!
Just a little change for the end user and you save a bunch of calcs
Remember "simple is better than complex"