Notice issued under section 148

Hi,

Can anyone guide me as received a notice under section 148 of income tax. Can i seek extension to reply to the notice as i was away when notice was received and its due date is nearing.

Is there any format available to seek extension or i can write a letter and go to income tax office and submit them letter requesting extension.

Also, can i ask them the reason for sending the notice as return was already filed or i need to make this a formal correspondence.

Is it necessary to file reassment return or i can ask them to consider same ITR as final one.

Rgds

A