With your cusror in the offending field, right click and toggle field codes.
The field will change from something like
<<mydate>> to {Mergefield Mydate}
Before the final bracket add the switch eg
{Mergefield Mydate \@ "dd/MM/yy"}
With the cursor still in the field, press F9 and the field will update and
revert to the previous display and your date should be corrected.
This is not programming nor rocket science, but the basic tools of mail
merge.
--
<>>< ><<> ><<> <>>< ><<> <>>< <>><<>
Graham Mayor - Word MVP
<>>< ><<> ><<> <>>< ><<> <>>< <>><<>