[{"_id":"ID_GOES_HERE","fileID":"0pdn3jdndndj3msms","fileName":"Item List","items":[{"tagNo":2,"status":0,"tagID":"kLawOURVpz1IIjoQ2fhCvy7NM","tagUnit":5},{"tagNo":2,"status":0,"tagID":"kLawOURVpz1IIjoQ2fhCvy7NM","tagUnit":8},{"tagNo":2,"status":0,"tagID":"pOawOURVpz1IIjoQ2fhCvy7w3","tagUnit":81},{"tagNo":4,"status":0,"tagID":"kLawOURVpz1IIjoQ2fhCvy7NM","tagUnit":904},{"tagNo":3,"status":0,"tagID":"pOawOURVpz1IIjoQ2fhCvy7w3","tagUnit":24},{"tagNo":2,"status":0,"tagID":"pOawOURVpz1IIjoQ2fhCvy7w3","tagUnit":35},{"tagNo":1,"status":0,"tagID":"kLawOURVpz1IIjoQ2fhCvy7NM","tagUnit":11},{"tagNo":2,"status":0,"tagID":"kLawOURVpz1IIjoQ2fhCvy7NM","tagUnit":30}]}]

db.collection.aggregate([{$match:{"fileID":"0pdn3jdndndj3msms","items.tagNo":2}},{$project:{"items":{$filter:{input:"$items",as:"item",cond:{$eq:["$$item.tagNo",2]}}}}}])