See the documentation here: https://docs.mendix.com/refguide/parse-and-format-date-function-calls
and here: https://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html
Also make sure that the value is not empty. So do check that before doing the parsing.
Regards,
Ronald
Latest versions of model reflection allow you to specify a display pattern for the token. You also need a recent version of the email with templates module. For each token you can then set a display pattern.