Sorry, check out the Common Abbreviations thread up at the top of this forum. Credit Scoring 101 is also up there and is your survival guide, and Frequently Requested Threads has examples of different types of letters, etc.
The person who does the work is you!

It involves doing some research in those threads up above, and some time writing letters, but it amazes me how many people come here after they tried to get someone else to fix their credit, and it wound up even worse.
Finally, what you are describing with your friend is called "piggybacking." It started out with spouses being authorized users on one another's cards, and then kids going AU on their parents' cards, and then it just went completely out of control. It is now so bad that the scoring system is being revised to eliminate the benefit to the AU. So even if it helped you out in the first month or so, once FICO 08 (the new scoring system) kicks in, the party's over. It is actually going to hurt a lot of people who did this in good faith, for instance, older housewives who were AU's on their husbands' cards. (This would include me.) And of course, it affects others as well.
Depending on where you're starting from, you shouldn't need to do that. And frankly, it involves a lot of risk for people to do this --it might be one thing for family, but not so for friends or strangers.
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007