How to merge an object inside another object

I don't know if the question is right, but I want to do the following, I want the properties of "variable" to become part of the variable day.

The object being as follows: {seg: 60, min:1, dias: 7, semana: 1}

Remaining the object of the following way: Take into consideration that the object inside the object could be anyone and it does not have to be the property "variable" for what I would like to make it dynamic, reason why an arrangement like delete dia.variable and later to merge would not serve me.

With the code that I show you I have only obtained that the result is: {seg: 60, min:1, variable:{dias: 7, semana: 1}, dias: 7, semana: 1}

Any ideas on how I could do it more efficiently, and above all, do it.

const dia = {seg: 60, min:1, variable:{dias: 7, semana: 1}}
let varia = {}
let newDia = {}

const processJson = () => {
    Object.entries(dia).map(([name, value]) => {
        if(typeof(value) === 'object'){
            varia = value
            newDia = {...dia, ...variable}
        }
    })    
}

processJson()

This is a universal method for flatting any object with 2 levels deep. It uses the array reduce method and the Object.keys() function:

const dia = { seg: 60, min: 1, variable: {dias: 7, semana: 1} }

function flatObject(o) {
  return Object.keys(o).reduce((result, key) => {
  
    // If there is a nested object, flat the object
    if (typeof o[key] === 'object' && ! Array.isArray(o[key]) && o[key] !== null) {
      for (const inKey in o[key]) {
        result[inKey] = o[key][inKey];
      }
    }
    // Just copy the value
    else {
      result[key] = o[key];
    }
    
    // Return accumulator
    return result;
  }, {});
}

console.log(flatObject(dia))