How to apply for Xinzhou social security card at the post office?

I can't. The new company can only apply for a new pension insurance for you, but the social security law stipulates that everyone can only have one pension insurance, so you must go through the formalities of transferring the pension insurance relationship, otherwise there will be a lot of trouble in the future.

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.