How to put a link in my route title?
In you routing.yml change _title to _title_callback as below:

amap.distribution_inscription_many_form:
  path: '/amap/editPlanningMany'
  defaults:
    _form: '\Drupal\amap\Form\DistributionInscriptionManyForm'
    _title_callback: '\Drupal\amap\Controller\TitleController::title'
  requirements:
    _permission: 'edit distribution inscription entities'


Create a "TitleController" controller in you amap module unser "src/Controller"

TitleController.php

&lt;?php

namespace Drupal\amap\Controller;

use Drupal\Core\Controller\ControllerBase;

class TitleController extends ControllerBase {

  public function title() {
    return t('Update Planning &lt;a href="/amap/editPlanningOne"&gt;Click here&lt;/a&gt;');
  }

}


Now your title will be callable from the controller and you can give whatever that likes you here.