In this issue, you could use WHMCS Bridge plugin, then you don’t need to edit the header and footer to match your website.
If you want to use a custom WHMCS template to match the header and footer like your website and you don’t know how to edit the header and footer to match your website, then you need to hire someone else WHMCS expert to do those based on your needs and requirements.
However, you will get the header content in the header.tpl file and the footer content in the footer.tpl
In this issue, you need to contact with WHMCS support. Because we are not the developer of WHMCS. We have just provided WHMCS template for FREE of cost with our Theme by customizing WHMCS default six template’s header, footer, and color based on our HTML Theme.