Try the settings for the project and then the language tab, this allows for setting the default formatting of you date and time. Not sure though if the needed format can be achieved as I never tried this specific format.
If I interpret you correctly, you're trying to set a default value for a domain model attribute. You can do that in the attribute settings, and the format should be like this:
If you need to have a bit more control about the default date, e.g. two weeks in the future. Than i would advice using an Event handler. With an after create microflow you can assign a dynamically default value.