How to check for similar collection withing a collection then add or update mongodb

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MongoDB

Node.js

so i am trying to select a specific array from my department-> dStock collection.
i want to select it like i would any other data fields in my initial collection and edit or delete it or simply check for duplicates before adding info.

What I have tried:

let departmentStock = await Department.findOne({
 departmentName,
 departmentProperty,
 dStock: { itemCode, itemName }, 

i am not sure about the last line above, here i want to filter by department stock(dStock) then edit this information and reinsert it or simply update it });

as shown below dStock is an array of items withing the department Module.

const DepartmentSchema = new mongoose.Schema(
  {
    departmentName: { type: String, required: true, trim: true, minlength: 3 },
    dStock: [
      {
        itemCode: { type: String, required: true, trim: true, minlength: 3 },
        itemName: { type: String, required: true, trim: true, minlength: 3 },
        itemQty: { type: Number, trim: true },
      },
    ],
    dOpenTime: { type: Date, trim: true, minlength: 4 },