[{"_id":ObjectId("630652a5490491c37dccff9c"),"address1":7,"balance":[{"date":5,"value":11}],"clientCode":1,"clientRef":2,"dateOfBirth":10,"exec":9,"fileNumber":"name","instalmentAmount":12,"name":3,"phoneNumber1":4,"phoneNumber2":5,"phoneNumber3":6,"postcode":8}]

db.collection.update({fileNumber:"name"},[{$replaceRoot:{newRoot:{$cond:[{$in:["value",{$ifNull:["$balance.value",[]]}]},"$$ROOT",{$mergeObjects:[{clientCode:1,clientRef:2,name:3,phoneNumber1:4,phoneNumber2:5,phoneNumber3:6,address1:7,postcode:8,exec:9,dateOfBirth:10,instalmentAmount:12,},"$$ROOT",{balance:{$concatArrays:[{$ifNull:["$balance",[]]},[{value:11,date:1}]]}}]}]}}}],{upsert:true})