ashfaan10 Hello Heather here I hope you are well. The best way to do this is using the existing ad code that you have as this will ensure your data is preserved within these ad placeholders and then hardcode the ad code within your site. Is your site built on wordpress? If so this article can guide you https://wordpress.ezoic.com/how-to-hard-code-placeholders-into-a-wordpress-theme/
If you have any left over ad placeholders that don't fit into the boxes that you have mentioned I would first of all recommend adding in a disclosure notice through the chrome extension so that you can recreate a similar look to your site with these additional ad placeholders. If you would prefer you can also delete the ad placeholders. Please note that both of these steps are likely to impact your sites earnings. many thanks