Elementor does not have its own snippet slot. One install in the WordPress head covers every Elementor page on the site.
1. Copy the snippet
In Stellar, open the project for this site and copy the snippet from your domain settings. Leave Anti-Flicker on if you are running visual tests. Direct head install is what makes that work. How anti-flicker works.
2. Paste it on Elementor
Add the snippet to the WordPress head with WPCode (Insert Headers and Footers), or paste it in header.php inside <head>.
If you use a child theme, put it in the child theme so a theme update does not remove it.
Do not also paste it into an Elementor HTML widget. That only covers one page and loads too late.
Save, then open a published page. The Elementor editor preview is not a valid check.
If you use WP Rocket, NitroPack, Autoptimize, or a similar plugin, exclude stellar.js and d3niuqph2rteir.cloudfront.net from JavaScript minify, combine, and defer. Those plugins will break the snippet if they rewrite it.
3. Confirm it loaded
Open a published page in a private browser window. Editor and draft previews often hide the snippet.
Open developer tools and go to the Network tab.
Reload and look for stellar.js. If that request is there, the install is done.
If it does not load
Check a live page, not the Elementor canvas.
Cache and optimization plugins are the usual reason it fails to load. Exclude the snippet, then clear cache.
Install it once. A plugin plus header.php means two copies.