Why don't store properly on nested object MongoDB - node.js

Question

I need to update a document with an object, but my approach looks like don't apply the changes on DB, can someone explain me what I'm doing wrong, please?
let dishes = await this.dishesModel.find({});
let dishesPromise = dishes.map((dish, i) => {
dish.ingredients.forEach((item) => {
if (item?.item) {
if (item['item']['unit']['_id'].toString() === payload._id) {
item['item']['unit'] = unit;
}
}
});
return dish.save();
});
await Promise.all(dishesPromise)
In the above code I get unit previously and the objective is to use this unit in: item['item']['unit']
A dish document looks like:
{
"_id": { "$oid": "62cc00bfad995c0e7d8bbb7d" },
"name": "Bologne pasta",
"price": 6.99,
"ingredients": [
{
"quantity": 3,
"item": {
"_id": { "$oid": "62cbe92821464145f0eb280e" },
"name": "Cow beef",
"code": "meat-01",
"price": 9.99,
"value": 100,
"internal": true,
"categories": [
{
"_id": { "$oid": "62cbe83221464145f0eb27ea" },
"name": "Meat",
"disabled": false
}
],
"unit": {
"name": "GRAMASO 2",
"abbr": "gr.",
"_id": { "$oid": "62befe5ff6f95cf46a4cfe5b" }
},
"disabled": false,
"__v": 0,
"translation": { "es": { "name": "Carne de vaca" } }
}
},
{
"quantity": 2,
"item": {
"_id": { "$oid": "62cbea3121464145f0eb283a" },
"name": "Tomato",
"code": "vegetable-02",
"price": 1.5,
"value": 20,
"internal": true,
"categories": [
{
"_id": { "$oid": "62cbe82921464145f0eb27e6" },
"name": "Vegetables",
"disabled": false
}
],
"unit": {
"name": "GRAMASO 2",
"abbr": "gr.",
"_id": { "$oid": "62befe5ff6f95cf46a4cfe5b" }
},
"disabled": false,
"__v": 0,
"translation": { "es": { "name": "Tomate" } }
}
},
{
"quantity": 1,
"item": {
"_id": { "$oid": "62cbee5621464145f0eb2865" },
"name": "Spagetti",
"code": "pasta-01",
"price": 1.5,
"value": 100,
"internal": true,
"categories": [
{
"_id": { "$oid": "62cbee3e21464145f0eb285f" },
"name": "Pasta",
"disabled": false
}
],
"unit": {
"name": "GRAMASO 2",
"abbr": "gr.",
"_id": { "$oid": "62befe5ff6f95cf46a4cfe5b" }
},
"disabled": false,
"__v": 0,
"translation": { "es": { "name": "Espaguetti" } }
}
}
],
"categories": [
{
"_id": { "$oid": "62cbe84721464145f0eb27f6" },
"name": "Italian",
"disabled": false,
"translation": { "en": { "name": "Italiana" } }
}
],
"__v": 0,
"translation": { "es": { "name": "Pasta con salsa boloñesa" } }
}
At last, the changes are not reflecting on DB, but I don't figure out what's wrong.