alternative to an if else inside a for loop

Question

Currently my code is working properly but I would like to have an alternate version of my code example without the if else. I would like to use functional programming with functions such as find but I am a bit stuck with the second loop inside the first loop.

The aim of the code is to update the array of tasks when either a task or a subTask when their id matches a given id. The updated task (or subTask) should remain at the same position in the array of tasks (or in the array of subTasks)

To simply things:

const idToSearch; let index; let subIndex; 
for (const task of tasks){ 
  if (task.id === idToSearch && stuff to validate task){
     const task = update(task, parameters);
     tasks.splice(index, 1, task);  
  }
  else if (task.hasSubTasks){
     for (const subTask of task.subTasks){
        if (subTask.id = idToSearch && stuff to validate subtask){
           const subTask = update(subTask, parameters);
           task.subTasks.splice(subIndex, 1, subTask);
           tasks.splice(index,1,task);
           return;
        }
        subIndex++;
     }  

 }   
 index++; 
}

Could you give me some pointers?

Edit: I just reformulated the question, I was not precise enough.

Edit2: the update function is pure. It takes the task (or subTask) and parameters and returns the updated task / subTask.