As I change the date format into <access date>, it is currently 12/03/2017 and should be 12 Mar 2017.
Endnote at present does not have an option for automatically changing the format of dates. You might submit this request on the Product Suggestion section of the forum.
In the meantime, the best you can do is use Endnote’s “Find and Replace” to change the dates. It might be helpful to presort the library records by date and display the data field in the library window to facilitate identifying and changing dates.