[{"_id":ObjectId("55528f000000000000000000"),"contractId":"55528fxxxxxxxxxxxx","field1":[{"name":"example","backendData":{"map":{"7552":"RTEST","3511":"TESTR","5312":"JKTLE","5310":"INVTS"}},"data":{"defaultOrder":["7552","3511","5312","5310"]}}]}]

db.collection.update({/** match the doc by _id*/"_id":ObjectId("55528f000000000000000000")},[{/** rebuild field1*/"$set":{"field1":{"$map":{"input":"$field1","in":{/** merge what's there plus filtered map plus new object*/"$mergeObjects":["$$this",{"backendData":{"map":{"$mergeObjects":[{"$arrayToObject":{"$filter":{"input":{"$objectToArray":"$$this.backendData.map"},"as":"stuff","cond":{/** keep everything except object with 7552 key*/"$ne":["$$stuff.k","7552"]}}}},{"5355":"IRZTS"}]}}},{"data":{"defaultOrder":{"$concatArrays":[{"$filter":{"input":"$$this.data.defaultOrder","as":"someNum","cond":{/** keep everything except 7552*/"$ne":["$$someNum","7552"]}}},["5355"]]}}}]}}}}}])