Database
[{"_id":ObjectId("64390a7196f544082a671469"),"name":"Sydney","issues":[{"vol":"2","num":"1","freq":5},{"vol":"1","num":"2","freq":7}]},{"_id":ObjectId("64390a8796f544082a67146a"),"name":"Canton","issues":[{"vol":"2","num":"2","freq":9},{"vol":"1","num":"3","freq":9},{"vol":"2","num":"1","freq":11}]}]
Query
db.collection.update({"_id":ObjectId("64390a8796f544082a67146a"),"issues.vol":"2","issues.num":"1"},{"$set":{"issues.$.freq":45}})