db={"FormData":[{"_id":ObjectId("5e3c27bf1ef77236945ef07b"),"eed12747-0923-4290-b09c-5a05107f5609":"20200206","bd637691-782d-4cfd-8624-feeedfe11b3e":"20200206_1@mail.com"}],"Form":[{"_id":ObjectId("5e3c27bf1ef77236945ef07b"),"Fields":[{"FieldID":"eed12747-0923-4290-b09c-5a05107f5609","Title":"Phone"},{"FieldID":"bd637691-782d-4cfd-8624-feeedfe11b3e","Title":"Email"}]}]}

db.FormData.aggregate([{$match:{"_id":ObjectId("5e3c27bf1ef77236945ef07b")}},{$project:{kv:{"$objectToArray":"$$ROOT"}}},{$unwind:"$kv"},{"$lookup":{"from":"Form","let":{uuid:"$kv.k"},"pipeline":[{$match:{"_id":ObjectId("5e3c27bf1ef77236945ef07b")}},{"$unwind":"$Fields"},{$match:{$expr:{$eq:["$$uuid","$Fields.FieldID"]}}},{$project:{_id:false,k:"$Fields.Title"}}],"as":"formLookup"}},{$unwind:"$formLookup"},{$project:{kv:{"$mergeObjects":["$kv","$formLookup"]}}},{$group:{_id:"$_id",kv:{$push:"$kv"}}},{"$project":{newDoc:{"$arrayToObject":"$kv"}}},{"$replaceRoot":{"newRoot":{"$mergeObjects":[{"_id":"$_id"},"$newDoc"]}}}])