[{"pickup_date":ISODate("2020-08-11T00:38:18Z")},{"pickup_date":ISODate("2020-08-11T04:38:18Z")},{"pickup_date":ISODate("2020-08-05T04:38:18Z")},{"pickup_date":ISODate("2020-02-05T04:38:18Z")}]

db.collection.aggregate([{$match:{$expr:{$gte:["$pickup_date",{"$subtract":["$$NOW",604800000]}]}}},{$group:{_id:{year:{$year:"$pickup_date"},month:{$month:"$pickup_date"},day:{"$dayOfMonth":"$pickup_date"}},count:{$sum:1}}},{$project:{count:1,_id:0,event_date:{"$concat":[{"$toString":"$_id.day"},"/",{"$toString":"$_id.month"},"/",{"$toString":"$_id.year"}]}}}])