I have received a outstanding demand us 1431a

The E-processing window for the assessment u/s. 143(1a) would open within 4/5 working days from the date of order; so wait for any response for disagreement.    In case you agree, pay the demand.

Thanks, Sir for your response.
Actually, there is a tax credit mismatch as not whole tax is reflected on 26AS. I have requested multiple times my employer to update the same. They are also not providing original form 16. Instead, they are proving a manual form 16 with a stamp.  So how to proceed?

CPC will not give you credit for any TDS which is not reflected in form 26AS. So either get back the amount from employer or complaint against him to ITO (TDS); but the demand need to be paid.

Can we seek more time from CPC as revising TDS will take time. So how to respond the demand is there any option to seek more time for rectification?

Unless you pay the demand, the interest will get on added/accrued over it. So, if you are sure that the employer is going to pay the TDS amount and file corresponding TDS return, no need to pay the demand.

Once you get revised form 16 as downloaded from TRACES site, you can file rectification request.

Employer will not revise its TDS return so easily and give yoy tds credit. I can solve your problem. may contact me. CA umesh kumar- 9717597230