Additiona to Custom Form

You will be adding a new feature to an existing large online form already created in Wordpress. The additional elements are as followed: 1. In 1 area of the form, there will be a checkbox option where if it is clicked, it will automatically complete the textarea below with default text 2. There will be a 'preview' button added where the user can see the submission before it is hit. There will also be a 'send' option from the preview.