@Hailun Feng , since IRS has already transferred/ attached the EIN to the C-Corp. , you are done ---- EIN is used for filing employee tax deposits as also the entity's own return -- it is only a tax ID (just like ITIN for non-resident or those not eligible for SSN ) . .No worries for you .
If by chance you are not convinced of this position, please consider visiting the nearest IRS office and discuss this situation -- they are generally quite helpful.
