hudakchullu,
very easy I had RFE on tb skin test too. find a USCIS approved surgeon near you and call them first to ask them that you need just the tb-skin test only (no regular full immigration medical) and make sure you tell them that INS/USCIS has requested just the regular tb-skin test and not all tests. ask them how much does it cost? and it should not be more than 50$ if so find another doctor in your zipcode, its ok if you drive 50miles to find a cheaper doc.
tell the doc to get the test done and mark the I-693 medical form with his signature and comments on tb skin test. for ex if its negative it will be good if doc can write no reaction, and if its positive he should write how many "mm". after this tell doc office to put the signed I-693 form, make sure you sign the I-693 too and fill in your name, address, ssn and other details required etc adn then seal it in a doctor office letterhead with their seal or stamp on the back on the seal.
mail this back to USCIS to the correct po box address, note if you are sending to TSC then refer to correct po box address the one on your RFE is most probably not right for TSC. I will give you some sample threads where you can see issues and problems faced by me and several others on wrong po box address mentioned on RFE by USCIS.
make sure you use correct address and then finall but most important send an express mail from USPS and CHECK BOX FOR "NO SIGNATURE REQUIRED ON DELIVERY". good luck hope this helps.
http://www.immigrationportal.com/showthread.php?t=264773