CrossOver respects the Region setting of the Formats tab of the Language & Text (formerly International) preference pane, except if it's set to Custom. That is, if you select one of the presets in that pane, CrossOver will format dates and numbers according to that region. If you customize the format manually, CrossOver will probably not format dates according to your settings.
You can also customize the settings using the Windows registry. Use the Run Command dialog to launch "regedit" for the bottle of your choice. Within regedit, navigate to HKEY_CURRENT_USER\Control Panel\International. There, you can set the format for dates and numbers.
It seems that it gets the date and region information from mac, knowing mac there is no easy access to bios or EFi there so changing the date there will not be easy. But it seems that changing the date in macOS should be the solution.