Database
[{"_id":ObjectId("615e3ddece93c870aca4e465"),"assembly":[{"_id":ObjectId("615e3ddece93c870aca4e466"),"SN":24,"Model":"J240","Job":1234,"Revision":"A","Version":1}],"assyHistory":[],"subAssemblies":[{"_id":ObjectId("615e3deace93c870aca4e467"),"SN":19,"Model":"P500"}]}]
Query
db.collection.update({"subAssemblies._id":ObjectId("615e3deace93c870aca4e467")},{$pull:{subAssemblies:{_id:ObjectId("615e3deace93c870aca4e467")}}})