Section 3. If, at the time fixed for the beginning of the term of the President, the President elect shall have died, the Vice President elect shall become President. If a President shall not have been chosen before the time fixed for the beginning of his term, or if the President elect shall have failed to qualify, then the Vice President elect shall act as President until a President shall have qualified; and the Congress may by law provide for the case wherein neither a President elect nor a Vice President elect shall have qualified, declaring who shall then act as President, or the manner in which one who is to act shall be selected, and such person shall act accordingly until a President or Vice President shall have qualified.
The amendment seems to assume there is some mechanism for proving qualification but doesn't say what it is. Odd oversight it seems.
The President Elect has to present sufficient evidence to Congress that he meets these requirements or he will not be allowed to serve. A proper birth certificate would surely be evidence of place of birth and legal age as well as the citizenship of both parents. Since the Constitution demands that this be done, was it? If so, we the people have a right to see what evidence was accepted by our representatives in Congress don't we? I don't think it was done. I don't think we have a legal President and if the new Congress doesn't get to the bottom of this soon, I don't think we have a legal government, period.