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

<label class="wizard-btn wizard-btn-upload-file {{if uploading 'disabled'}}">
  {{#if uploading}}
    {{i18n "wizard.uploading"}}
  {{else}}
    {{i18n "wizard.upload"}}
    {{d-icon "upload"}}
  {{/if}}

  <input disabled={{uploading}} type="file" accept="{{field.file_types}}" style="visibility: hidden; position: absolute;" />
</label>

{{#if field.value}}
  <a href="{{field.value.url}}" class="filename">
    {{#unless isImage}}
      {{field.value.original_filename}}
    {{else}}
      <img src={{field.value.url}}  class="wizard-image-preview">
    {{/unless}}
  </a>
{{/if}}