Found the solution myself.
Sharing the text here just for information.
valueexpression=CONCAT(YEAR({plannedStartDate}),'-',IF(MONTH({plannedStartDate})<10,CONCAT('0',MONTH({plannedStartDate})),MONTH({plannedStartDate})),'-',IF(DAYOFMONTH({plannedStartDate})<10,CONCAT('0',DAYOFMONTH({plannedStartDate})),DAYOFMONTH({plannedStartDate})),'T',IF(HOUR({plannedStartDate})<10,CONCAT('0',HOUR({plannedStartDate})),HOUR({plannedStartDate})),':',IF(MINUTE({plannedStartDate})<10,CONCAT('0',MINUTE({plannedStartDate})),MINUTE({plannedStartDate})),':',IF(SECOND({plannedStartDate})<10,CONCAT('0',SECOND({plannedStartDate})),SECOND({plannedStartDate})),'.',IF(MILLISECOND({plannedStartDate})<10,CONCAT('00',MILLISECOND({DE:Announcements Send Date Time})),IF(MILLISECOND({plannedStartDate})<100,CONCAT('0',MILLISECOND({plannedStartDate})),MILLISECOND({plannedStartDate}))),'Z')