[{"attendanceSheet":[{"_id":"60dd77c14524e6c116e16aaa","workerFirstName":"MEGHRAJ","workerSurname":"JADHAV","workerId":"2036","attendances":[{"_id":"6130781085b5055a15c32f2u","workerId":"2036","workerFullName":"MEGHRAJ JADHAV","workerType":"Employee","Date":"2022-10-01T00:00:00.000Z","createdAs":"ABSENT"},{"_id":"6130781085b5055a15c32f2u","workerId":"2036","workerFullName":"MEGHRAJ JADHAV","workerType":"Employee","Date":"2022-10-02T00:00:00.000Z","createdAs":"ABSENT"}]},{"_id":"60dd77c24524e6c116e16c0f","workerFirstName":"SANJAY","workerSurname":"DUTTA","workerId":"2031","attendances":[{"_id":"6130781a85b5055a15c3455y","workerId":"2031","workerFullName":"SANJAY DUTTA","workerType":"Employee","Date":"2022-10-02T00:00:00.000Z","createdAs":"ABSENT"}]}]}]

db.collection.aggregate([{$set:{attendanceSheet:{$map:{input:"$attendanceSheet",as:"external",in:{$mergeObjects:["$$external",{attendances:{$reduce:{input:"$$external.attendances",initialValue:[],in:{$concatArrays:["$$value",[{_id:"$$this._id",createdAs:"$$this.createdAs",Date:"$$this.Date"}]]}}}}]}}}}}])