What is the Procedure asking Extra time or Submitting for Defective Notice reply u/s 139(9)

Hello Everyone,  

One of our client got notice u/s 139(9), due date is 05.12.2021, we couldn't give any response as on that day Now the submit response button is disabled as on today such as 10.12.2021 , how can we ask for Due date extension for reply.

Screeshot of Disabled for submit button as attached.

Please suggest us.  

Thanks in Advance