db={"Test1":[{"_id":"kcXtyaB7jGPw9Ks","dateCreated":"2022-07-12T13:09:16.270Z","dateModified":"2022-07-12T13:09:16.270Z","data1":1,"data2":100,"data3":5,"createdBy":"xQQrzRgi8","updatedBy":"56sgAeKfx"}],"Test2":[{_id:"xQQrzRgi8",fullName:"test name created"},{_id:"56sgAeKfx",fullName:"test name update"}]}

db.Test1.aggregate([{$lookup:{from:"Test2",localField:"updatedBy",foreignField:"_id",as:"updatedByName",},},{$lookup:{from:"Test2",localField:"createdBy",foreignField:"_id",as:"createdByName",},},{$set:{updatedBy:{$first:"$updatedByName.fullName",},},},{$set:{createdBy:{$first:"$createdByName.fullName",},},},{$project:{updatedByName:0,createdByName:0,},},])