[{"postId":ObjectId("62dffd0acb17483cf015375f"),"userId":ObjectId("62dff9584f5b702d61c81c3c"),"state":[{"id":ObjectId("62dffc49cb17483cf0153220"),"notes":"these are my custom notes!","lvl":3,},{"id":ObjectId("62dffc49cb17483cf0153222"),"notes":"hello again","lvl":0,},]},]

db.collection.update({postId:ObjectId("62dffd0acb17483cf015375f"),userId:ObjectId("62dff9584f5b702d61c81c3c"),state:{$elemMatch:{id:ObjectId("62dffc49cb17483cf0153220"),lvl:0}}},{$set:{/** add your update fields*/"state.$.notes":"new note"}},{returnNewDocument:true})