Database
[{"_id":ObjectId("5c05984246a0201286d4b57a"),"_a":[{"_onlineStore":{}},{"_p":{"s":{"a":{"t":[{"dateP":"20200-09-20","l":"English","size":"XXL"}]}}}}]}]
Query
db.collection.update({},{$set:{"_a.$[a]._p.s.a.t.$[x].dateP":"2022-01-02"}},{arrayFilters:[{"a._p":{$exists:true}},{"x.dateP":"20200-09-20"}]})