discourse-custom-wizard/assets/javascripts/wizard/templates/components/wizard-field-composer.hbs

{{wizard-composer-editor replyPlaceholder=field.placeholder
                         composer=composer
                         storeToolbarState=(action "storeToolbarState")
                         onPopupMenuAction=(action "onPopupMenuAction")
                         showUploadModal=(action "showUploadSelector")
                         groupsMentioned=(action "groupsMentioned")
                         cannotSeeMention=(action "cannotSeeMention")
                         importQuote=(action "importQuote")
                         togglePreview=(action "togglePreview")
                         afterRefresh=(action "afterRefresh")}}

<button class='wizard-btn primary toggle-preview' {{action 'togglePreview'}}>
  <span class="d-button-label">{{i18n togglePreviewLabel}}</span>
</button>