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.Form.aggregate([{$match:{"_id":ObjectId("5e3c27bf1ef77236945ef07b")}},{$lookup:{from:"FormData",localField:"_id",foreignField:"_id",as:"formLookup",pipeline:[{$project:{_id:0}}]}},{$set:{formLookup:{$objectToArray:{$first:"$formLookup"}}}},{"$replaceRoot":{"newRoot":{"$mergeObjects":[{$arrayToObject:{$map:{input:"$formLookup",in:{$mergeObjects:[{v:"$$this.v"},{k:{"$getField":{input:{$arrayElemAt:["$Fields",{$indexOfArray:["$Fields.FieldID","$$this.k"]}]},field:"Title"}}}]}}}},{_id:"$_id"}]}}}])