[{_id:1,services:[{id:"1",name:"Service 01",items:[{id:"1",name:"",qty:10},{id:"2",name:"",qty:10},]},{id:"2",name:"Service 02",items:[{id:"3",name:"",qty:10},{id:"4",name:"",qty:10},]},]},{_id:2,services:[{id:"1",name:"Service 01",items:[{id:"1",name:"",qty:10},{id:"2",name:"",qty:10},]},{id:"2",name:"Service 02",items:[{id:"3",name:"",qty:10},{id:"4",name:"",qty:10},]},]}]

db.collection.update({_id:2},{$set:{"services.$[].items.$[].qty":0}})