Hi Kumar Anish,

Word has a number of different methods of connecting to mail merge data sources, including DDE and OLE DB. Word 2002 and later use the OLE DB coonection by default, though you can change this (to DDE, for example). To work around a limitation in the OLE DB provider used to get data from Excel etc., when Word is connected to an OLE DB data source, it treats dates as if they are in the US mm/dd/yy format, regardless of the format in Excel, your regional settings etc. Applying a date format switch fixes that – and gives the mailmerge document the ability to format the date independently of whatever format is used in the data source.

To get the date format you want, you can add a formatting picture switch as follows:
• select the mergefield;
• press Shift-F9 to expose the field coding. It should look something like {MERGEFIELD MyDate} where 'MyDate' is your mergefield's name;
• delete anything appearing after the mergefield's name and add '\@ "dd-MMM-yy"' to the field, as in {MERGEFIELD MyDate \@ "d MMMM yyyy"}. With this switch your date will come out as '2 August 2008'. Other possible date formatting switches include:
. \@ "dddd, d MMMM yyyy";
. \@ "ddd, d MMMM yyyy";
. \@ "d MMM yyyy";
. \@ "dd/MMM/yyyy".
Note: Note: you can swap the d, M, y expressions around, but you must use uppercase 'M's for months – lowercase 'm's are for minutes.
• position the cursor anywhere in this field and press F9 to update it;
• run your mailmerge.

Please also refer the below link
http://www.congamerge.com/blog/latest-posts/december-2013/formatting-dates-numbers-in-word-templates

Regards,
Justin