Update an item of json file, with new value

I am using an external json file as payload to a POST request in Cypress, like this

cy.fixture('createUsers.json').then((requestBody) => {  cy.request('POST', /api/vi/createUsers, requestBody).then(function (res) {    localStorage.setItem('token', res.body.token);    localStorage.setItem('refreshToken', res.body.refreshToken);  });});

The json file looks like this

    {"carID": "HND","from": 1683579600000,"to": 1683579600000,"launched": true,"lftl": false,"dmtr": null,"acxzId": "HND_PRE"    }

I want to keep from and to fields as dynamic. This is Unix time stamp for today's date.

I am able to achieve this if I am passing payload in the fixture code, not via an external file like this

let testDate = Date.parse(new Date().toLocaleDateString("en-US"));cy.request('POST', /api/vi/createUsers,  {"carID": "HND","from": testDate,"to": testDate,"launched": true,"lftl": false,"dmtr": null,"acxzId": "HND_PRE"}).then(function (res) {  localStorage.setItem('token', res.body.token);  localStorage.setItem('refreshToken', res.body.refreshToken);});

So, how can I pass today's date, when I want to pass JSON payload using an external file?