Doesn't it already do that? What does it do if you enter 3 at "Enter number of computer sprecifications required?"; after you've entered the first details it looks like it should loop back to "Please Enter Brand?", although it's not so easy to tell with your brace abuse and lack of indentation.

Here's how braces and indentation are supposed to work:
Code:
somecode();
for(some;loop;stuff)
{
    loop();
    code();
}
This is much clearer than
Code:
somecode();
for(some;loop;stuff)
{{{{{{{{{{{{{{{{{{{{{{{{
loop();
code();
}}}}}}}}}}}}}}}}}}}}}}}}
and once you start getting into proper programming with multiple nested code blocks you'll find your current style extremely difficult to read. Programming's already hard enough, why make it harder?