db={orders:[{"_id":"wJNEiSYwBd5ozGtLX","orderId":52713,"retailerId":1320,"createdAt":ISODate("2020-01-31T04:34:13.790Z"),"status":"closed"},{"_id":"wJNEiSYwBd5ozGtLX2","orderId":52714,"retailerId":1320,"createdAt":ISODate("2021-03-31T04:34:13.790Z"),"status":"closed"}],users:[{"_id":"2gSznevqwkGTxLRvL","createdAt":ISODate("2018-04-10T08:33:13.455Z"),"username":"retailer@gmail.com","info":{"retailerId":1320,},"settings":{},"status":"active",}]}

db.users.aggregate([{"$lookup":{"from":"orders","let":{"rId":"$info.retailerId"},"pipeline":[{$match:{$expr:{$eq:["$retailerId","$$rId"]},createdAt:{$gte:ISODate("2021-03-01T00:00:00.000Z"),$lt:ISODate("2021-04-01T00:00:00.000Z")}}}],"as":"orders"}}])