I want to know if somebody fail to give step 1 within eligibilty period + 3month extension, when we can apply for a new application and what documents required?
To answer the OP's question you can apply for the step 1 immediately after your eligibility period expires, if you didn't take the step 1 in the eligibility period. It will be the same as if when you applied the first time except without the application for ecfmg certification.