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

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