Shortening down @supermanPunch Approach with the dot as any char as seperator:

\b(\d{2}.){2}\d{2,4}\b
Or with some more restrictions to the delimeter:

\b(\d{2}[\/\\\-\.]){2}\d{2,4}\b
When later a parsing into DateTime is needed we can handle all formats in one go:
Ensure:

Assing Activity
arrFormats | DataType: String()
String Array =
{"dd/MM/yyyy","dd/MM/yy","dd\MM\yyyy","dd\MM\yy","dd-MM-yyyy","dd-MM-yy","dd.MM.yyyy","dd.MM.yy"}
Assign Activity:
myDateTime =
DateTime.ParseExact(YourSingleDateString, arrFormats, CultureInfo.InvariantCulture, DateTimeStyles.None)