CRA asking for copy of tax return they did not receive it and I cannot seem to generate another online delivery.Do I need to print it and mail it to them

I have already filed my tax return.  I have since received another T4 which I sent proper forms to correct.

CRA is now asking me for a corrected  return (they say they did not receive the original for which I have a confirmation number).  I have now tried to refile the return but the programme will not let me

Do I need to print and send it by mail.

thanks