Hello, Bagwani,
Thank you for reaching out to us.
To add a popup on your website offering an extra 5% off with a coupon, you can edit the header builder template via Elementor and add Newsletter element, then select a static block or a template with the desired content in settings of this element.
Please let us know the popup of which demo you like and we will create an example on your site.
The ideal size for a popup generally depends on the content you wish to include. However, a standard size that works well in most cases is 600×400 pixels. This size is large enough to catch attention while not overwhelming the rest of the page content.
Regarding offering an extra discount, please read this article https://woocommerce.com/document/coupon-management/ and contact woocommerce plugin to get further assistance – https://wordpress.org/support/plugin/woocommerce/ (this is independent of our theme).
Best Regards,
8Theme’s Team