Return filing under section 170A requires successor entities to submit ITR-A and a modified ITR-6 confirming compliance. Successor entities subject to an approved business reorganisation must file ITR-A to report income under the reorganisation scheme, providing detailed identifiers for filing and other successor and predecessor entities, assessment year and prior filing status, and particulars of the reorganisation order including issuing authority, order number and effective date. The form mandates uploading a modified ITR-6 reflecting adjusted income for the relevant assessment year and requires a verified declaration by an authorised signatory confirming compliance with the order's terms and conditions.