Hi,
If you use eazyBI add-on for Jira server, you could try using custom locales to change the way (by changing the format) how dates are displayed in the eazyBI reports.
https://docs.eazybi.com/display/EAZYBIJIRA/Custom+locales
N.B. it would affect all reports on the eazyBI account since custom locale is common for all reports in the account.
Martins / eazyBI team