JS / Mongoose - Access saved field that is removed in the schema

I have created a mongoose schema in the past with a certain field that I want to remove, or rather convert into an array now.

An instance of the original version looks something like this:

{ item: 'My awesome item' } // not showing other fields to save space

Which I want to change to something like this:

{ items: [ { name: 'My awesome item' } ] }

I changed the field in the schema to be an array of the above format. Now, in my database I still have old documents that have the item field and I want to convert them like so:

const models = await MyModel.find().exec()
for (const model of models) {
    if (model.item) {
        model.items = [ { name: model.item } ]
        model.item = undefined
        await model.save()
    }
}

Now the weird thing is, by printing my models I see that the docs I get through find() do indeed have the item field. However, mongoose already tried to pack it into the new schema so the model that I retrieve looks like this:

{ item: 'My awesome item', items: [] }

Hence, it already created the items field and still has the old item field. My problem now is that by mongoose packing it into the adjusted schema, I can't access the existing item field anymore. model.item is undefined although when printing the entire model object it shows.

Can anybody help how to solve this?