How to find the H1B case transfer service center?

My H1B visa valid till Feb 2019;

H1B Amendment Expired - 240 day expire in Dec

But last approved H1 amendment was expired on April 6th 2018 and so my employer confirmed that my legal work authorization will be valid till December 5th 2018;

H1B Extension pending

Due to which I have filed an extension on March 16th 2018 and still awaiting for the USCIS decision.

Case transferred from California to Other Service center

Recently September 28th 2018, my case was transferred from California center to another local office, but not sure which location it is.

How do we know the new location and is there an option to upgrade my case to premium if it’s moved to Nebraska.

Check USCIS case transfer data based on Transfer date

If your case was transferred on Sep 28, 2018, then it would have gone to Nebraska now.
See the USCIS updates: Workload Transfer Updates | USCIS

USCIS sends case transfer notice

You (or your employer attorney) will also receive a transfer notice which will clearly show the new service center name. Check with them if you want the exact center name.

H1B Upgrade to Premium at Nebraska Service Center

You can upgrade your application to ‘premium’ if it has ‘NO change’ and is now in Nebraska service center.