Wo kann ich meinen Text einschreiben?

<form method="post" id="sendtell-form">
                              <div class="form-group"> <textarea title="Tell" rows="3" class="form-control tell-input" name="tell" placeholder="Drop a few anonymous words!"></textarea> </div>
                              <div class="row">
                                 <div class="col-xs-12 col-sm-6 hidden-xs top-margin-10px">
                                    <a href="https://tellonym.de/register" class="normal">
                                       <div class="alert alert-info text-center" role="alert"> Create your own page and follow your friends.<br><b>Register now!</b> </div>
                                    </a>
                                 </div>
                                 <div class="col-xs-6 top-margin-10px"> <a href="https://tellonym.de/register" class="btn buttonblue-invert">Register</a> </div>
                                 <div class="col-xs-6 top-margin-10px"> <button type="submit" class="btn button">Send</button> </div>
                              </div>
                           </form>

document.querySelector('textarea[name=tell]').value = "dein text";