If the turnover of the registered taxable person exceeds Rs. 2 crore, then the Annual Return is required to be audited by a Chartered Accountant or Cost Accountant. Further, they also have to submit reconciliation statement in FORM GSTR-9C. If the turnover does not exceed Rs. 2 crore, the registered taxable person can himself compile the details in FORM GSTR-9 and submit the return.
(ICAI FAQ PUBLICATIONS 06-09-2017 RETURNS : FAQ NO. 51)