Nothing to do with portal administration but standard HTML can be used.
How to use an HTML <META> tag in the header to redirect to another page. The <META> tag goes in the <HEAD> section of your HTML document. The <META> tag on this page looks like:
<META HTTP-EQUIV="Refresh"
CONTENT="5; URL=html-redirect.html">
The "5" means to wait 5 seconds before redirecting. The "html-redirect.html" after "url=" is the URL of the page to which to redirect.