Add a downloadable execution field

Recently I found a code that creates a frame, along with a menu with the option to close the frame. I would like to add a downloadable field, but I have no idea how to do it. I will be grateful for the responses and collaboration of all.

Follow the code:

for (var GET = {
    ID: '',
    title: ''
}, query = window.location.search.substring(1).split('&'), i = 0, max = query.length; i < max; i++) if ('' !== query[i]) {
    var param = query[i].split('=');
    GET[decodeURIComponent(param[0])] = decodeURIComponent(param[1] || '')
}
if ('' != GET.ID && '' != GET.title) {
    var newTitle = GET.title.split('_').join(' ') + ' Blogger Theme',
        content = document.querySelectorAll('.content')[0],
        frame = document.createElement('iframe'),
        head = '<div class=\'preview_nav\'><a class=\'preview_logo\' href=\'/\'><img alt=\'ar-themes\' src=\'//1.bp.blogspot.com/-duMiwPm6ZMc/XCQj_nFOJQI/AAAAAAAAAYA/9-i6iduaUkU3bkYcpH-78OOYyzH0Gj-wgCPcBGAYYCw/s1600/logo-white.png\' alt=\'ar-themes Logo\'></a><h1 class=\'preview_title\' title=\'' + newTitle + '\'>' + newTitle + '</h1><a class=\'preview_close\' href=\'javascript:void(0)\' title=\'Close Frame\'><span>&times;</span>Close Frame</a><a class=\'preview_banner\' href=\'' target=\'_blank\' rel=\'nofollow\' title=\'Foodhall Responsive Food Blogger Theme\'><img src=\'https://3.bp.blogspot.com/-bb2siH6A2lA/Wr17qEpJCLI/AAAAAAAAGD0/8K37UBwJif0pDUW-JH0J5d_YXdDL061UQCLcBGAs/s1600/logo_new.png\' alt=\'Foodhall Responsive Food Blogger Theme\'></a></div>';
    frame.src = 'https://' + GET.ID + '.blogspot.com', content.innerHTML = head, content.appendChild(frame), document.querySelectorAll('.preview_close')[0].addEventListener('click', function() {
        document.querySelectorAll('.preview_nav')[0].classList.add('closed'), document.getElementsByTagName('iframe')[0].classList.add('closed'), setTimeout(function() {
            document.querySelectorAll('.preview_nav')[0].style.display = 'none'
        }, 300)
    })
} else window.location.href = '/';