You need to file form 2553 within 2 1/2 months from the start of the tax year you want the Scorp effective

See link:

https://www.irs.gov/businesses/small-businesses-self-employed/single-member-limited-liability-compan...

Are you asking about a state corporation number?

California?

"How to tax an SMLLC as an s-corp"

For Federal purposes, an S Corp isn't taxed.

For Federal purposes, you would only have a K-1 because someone prepared 1120S. How could they file 1120-S without EIN, because S Corp requires Payroll, so how did they run payroll without EIN?

So many questions. So few details.