Database
db={"teacher":[{"_id":ObjectId("64fee9b54273ac2234441225"),"teacherid":"64f1d72a4331bc8fc4c5930f","name":"Jackly"}],"users":[{_id:ObjectId("64f1d72a4331bc8fc4c5930f"),name:"Mark"}]}
Query
db.teacher.aggregate([{$match:{"teacherid":"64f1d72a4331bc8fc4c5930f"}},{$addFields:{teacherid:{$toObjectId:"$teacherid"}}},{$lookup:{from:"users",localField:"teacherid",foreignField:"_id",as:"student"}},{$unset:"name"}])