In your case you can purchase Notified Capital Gain bond to claim exemption u/s 54EC up to 30th day of September, 2020 or before filing your return u/s 139 (due date 30th November 2020) for F.Y 2019-20, whichever is earlier.
Date for Investment under section 54EC is extended to 30th September, 2020 via Notification No.35 /2020/ F. No. 370142/23/2020-TPL dated. 24th June, 2020