Database
[{"_id":"62bda37a4d28f5df2e0ab07f","qty":1,"dateCreated":ISODate("2022-06-30T13:22:02.368Z"),"price":4230.0,"ownership":"Owned","itemType":"EXPIRING_SOON","expirationDate":ISODate("2022-07-21T04:00:00.000Z"),"serialNumber":"20202868089"}]
Query
db.collection.aggregate([{"$addFields":{"expirationDate":{"$toDate":{"$subtract":[{"$toLong":"$expirationDate"},2592000000]}}}},{"$merge":{"into":"collection","on":"_id","whenMatched":"replace"}}])