Web Page Redirection Help

See, for example I've installed MyBB forums at my site hello.com
I've a page which shows 'Checking your browser stuff' let's name it checking.com (It's an HTML file).

So, what I want is I whenever a guy accesses hello.com, he first gets showed up with checking.com stuff and then back to hello.com in 5 seconds but the issue is I've already installed every stuff on hello.com and can't remove them.

Any help?