title: How to update controls of FormArray
body: <p>My form group code is as</p>
  
  <pre><code>this.myForm = this._fb.group({            
              branch_name: ['', [Validators.required]],
              branch_timing: this._fb.array([
                  this.initBranchTiming(),
              ])                                
          });
  
  initBranchTiming() {       
          return this._fb.group({
              day: ['', []],
              open_from: ['00:00:00', []],
              open_till: ['00:00:00', []]           
          });
    }
  </code></pre>
  
  <p>branch_name is updated by this code   </p>
  
  <pre><code>(&lt;FormControl&gt;this.myForm.controls['branch_name']).updateValue(this.branch_detail.branch_name);
  </code></pre>
  
  <p>Now i have to update the 'day' field of form array. what to do to update the 'day' field of form array branch_timing ?</p>