Since you mention that the date of birth in birth certificate, Aadhar, as well as passport is the same, and is the correct DOB, then it would be easier and better for you to approach the school and ask them to change their records and rectify the error.
According to the ICSE Regulations (which can be accessed on this link
), as you can see under point 7 (on page 11), it states that the Name and DOB must be certified by the Head of the School at the time of the entry. If the documents submitted by you as proof to the school for this, had the correct DOB (i.e. 30.08.2001) then the School should have certified and entered, that DOB.
Also see that sub point (ii) (a) says that (in case of discrepancies) the onus of responsibility in certifying the necessary changes/corrections lies with the Head of the School who shall be held liable in case of any legal dispute arising in future.
Kindly approach the school and ask them rectify their records as any information they certified and forwarded to the ICSE, as soon as possible.