[{"key":1,UpdateDt:ISODate("2021-04-06T02:07:47.231Z")},{"key":2,UpdateDt:ISODate("2021-04-06T22:07:47.231Z")},{"key":3,UpdateDt:ISODate("2021-04-06T12:07:47.231Z")}]

db.collection.aggregate([{"$addFields":{UpdateNewDt:{date:{$dateToString:{format:"%m/%d/%Y ,",date:"$UpdateDt",timezone:"GMT"}},hour:{$dateToString:{format:"%H",date:"$UpdateDt",timezone:"GMT"}},time:{$dateToString:{format:":%M:%S",date:"$UpdateDt",timezone:"GMT"}}}}},{$set:{"UpdateNewDt.hour":{$cond:{"if":{$gt:[{"$toInt":"$UpdateNewDt.hour"},11]},"then":{"$concat":[{$cond:[{$eq:[{"$toInt":"$UpdateNewDt.hour"},12]},"12",{$toString:{"$subtract":[{"$toInt":"$UpdateNewDt.hour"},12]}}]}," PM"]},"else":{"$concat":["$UpdateNewDt.hour"," AM"]}}}}},{$set:{"UpdateNewDt":{"$concat":["$UpdateNewDt.date",{"$arrayElemAt":[{"$split":["$UpdateNewDt.hour"," "]},0]},"$UpdateNewDt.time"," ",{"$arrayElemAt":[{"$split":["$UpdateNewDt.hour"," "]},1]}]}}},{$project:{UpdateDt:"$UpdateNewDt"}}])