You want to void the phone's warranty to "install" a completely useless (except to the people who sell them) little piece of plastic. Turn that "antenna booster" into a piece of artwork and next time ask before you waste your money on a 2 cent fraud. (Yes, that's what they cost the people who sell them - they're for sale for $20/1,000 on eBay all the time.)
If they worked, the phone manufacturers would put them in all their phones - and charge you $1 extra (or a lot more) for what basically would be free during the manufacturing process.
(The actual theory behind those things isn't taught in an EE course, it's taught in an MBA course - "there's one born every minute".)