Basically, don't use a regex: they are text processors, not programming languages, and while it might be possible to do what you want in a regex, it'd be horribly complicated and very difficult to understand or change later - when you met US date, or ISO instead of European date format for example. Or when you need to do it for a different language maybe.
A much better solution is use java code to convert the date to a Date object
] and then convert that to a string using the month name: How to Format Date to String in Java 8 [Example Tutorial] | Java67
A Regex is powerful tool, but so is a hammer: you should only use them when it is appropriate!