It is always better to mention facts only when we are applying for any certificate. If they search and find that already you have taken once, they will reject your application saying that you have hidden the facts. So never think of giving any wrong information. You can mention that you have taken it once. If it is possible you can say that there is a mistake in the name in the previous certificate. You can also mention that you are again applying with a view of getting the mistake corrected. Then you will get the corrected income certificate and you can apply for the scholarship using this certificate.