db={"Col1":[{"accountCode":"xyz","ITSM":"SNOW","anotherFieldxxx":"x"}],"Col2":[{"accountCode":"xyz","manager":"John","anotherFieldyyy":"yyy"}],"Col3":[{"accountCode":"xyz","admin":"Peter","anotherFieldzzz":"z"}]}

db.Col1.aggregate([{$project:{"anotherFieldxxx":0}},{$match:{"accountCode":"xyz"}},{$lookup:{from:"Col2",localField:"accountCode",foreignField:"accountCode",as:"Res2"}},{$lookup:{from:"Col3",localField:"accountCode",foreignField:"accountCode",as:"Res3"}},{$unwind:"$Res2"},{$unwind:"$Res3"},{$project:{accountCode:1,ITSM:1,manager:"$Res2.manager",admin:"$Res3.admin"}}])