Can't set value of an object in an API call

Question

I need my code to get the current rates using open-exchange-rates, use money.js to convert the currency and set the returned value to a JSON object. But the problem is that the JSON object stays the same it does not get modified:

 arr.prices.map(function(object) {
    // get current rate
    oxr.latest(function() {
       fx.base = "USD";
       fx.rates = oxr.rates;
       // convert usd to zmw
       let zmw = fx.convert(object["total"], { from: "USD", to: "ZMW" });
       // set new value
       object["total"] = zmw;
    });         
 });

Update after trying a promise: Still not working.

  arr.prices.map(function(object) {
    let p = new Promise((resolve, reject) => {
      oxr.latest(function() {
        fx.base = "USD";
        fx.rates = oxr.rates;
        let zmw = fx.convert(object["total"], { from: "USD", to: "ZMW" });

        if (zmw === undefined) {
          reject('Fail')
        } else {
          resolve(zmw);
        }
      });

    })

    p.then((zmw)=>{
      object["total"] = zmw;
    }).catch((error) => {
      console.log('Fail')
    })

  });