How to update field's default value on form rebuild?

I have built my form with a fieldset, which will rebuilt based on Add and Remove. The issue is I am unable to update the field's '#default_value' attribute, when a form is rebuilt by remove callback.

<?php
public function buildForm(array $form, FormStateInterface $form_state) {
  $i = 0;
  $num_rows = $form_state->get('num_rows');

  if (empty($num_rows)) {
    $num_rows = $form_state->set('num_rows', 1);
  }
  if ($form_state->get('rem')){
    $rem = $form_state->get('rem');
    $counter1 = range(1, $num_rows);
    $counter = array_flip($counter1);
    unset($counter[$rem]);
    $default = array_flip($counter);
    $input = $form_state->getUserInput();
  }

  for ($i = 0; $i < $num_rows; $i++) {
        
    if ($i == 0) {
      $form['dep_row']['#prefix'] = '<div id="dep-row-wrapper" class="row">';
      $form['dep_row']['#suffix'] = '</div>';

      $form['field_add_dep'] = [
        '#type' => 'submit',
        '#value' => t('Add Dependent'),
        '#submit' => array('::addOne'),
        '#limit_validation_errors' => array(),
        '#ajax' => [
          'callback' => '::addmoreCallback',
          'wrapper' => 'dep-row-wrapper',
        ],
        '#attributes' =>  array('class' =>  array('add-dep-bt')),
      ];
    }
    if ($i > 0) {

      $month_name = 'field_dob_dep_month_' . $i;
      

      if (isset($default)) {
        $m_default = 'field_dob_dep_month_' . $default[$i];
      }

      $form['dep_row'][$i] = [
        '#type' => 'fieldset',
      ];

      // Month
      $form['dep_row'][$i][$month_name] = [
          '#type' => 'textfield',
          '#title' => t(''),
          '#maxsize' => 2,
          '#size' => 10,
          '#maxlength' => 2,
          '#placeholder'  =>  t('MM'),
          '#default_value' => ,      
      ];

      $form['dep_row'][$i]['actions']['remove_name_' . $i] = [
        '#type' => 'submit',
        '#value' => t('(remove_' . $i),
        '#submit' => array('::removeCallback'),
        '#limit_validation_errors' => array(),
        '#ajax' => [
            'callback' => '::addmoreCallback',
            'wrapper' => 'dep-row-wrapper',
        ],
        '#attributes'  =>  array('class' => array('remove', 'dep-remove', 'dep-remove-' . $i))
      ];
    }
  }
}


public function removeCallback(array &$form, FormStateInterface $form_state) {
  $triggerdElement = $form_state->getTriggeringElement();
  $raw_element = explode('-', $triggerdElement['#attributes']['data-drupal-selector']);
  $element = $raw_element[count($raw_element) - 1];
  if (!in_array('spouse-remove' , $htmlIdofTriggeredElement)) {
    $name_field = $form_state->get('num_rows');
    if ($name_field > 1) {
      $remove_button = $name_field - 1;
      $form_state->set('num_rows', $remove_button);
      $form_state->set('rem', $element);
    }
    $form_state->setRebuild();
  }
}
?>