If my old employer said they can't assist to correct my W-2, how should I file W-2C?

What's wrong with your W2?

They didn’t include my final check. 

When did you get the final check?  Was it over year end?  Maybe it will be on a W2 for 2022 next year.

I don’t think so, it was issued in February. 

February 2021 or this year?  Maybe you are not adding up the right paystubs.  Like maybe the first one was really for 2020?  Or you are not adding them up right.  The W2 usually does not match the gross amount on your paystubs.  There can be several pretax items that affect it.  

Did the employer say the W2 is right or do they agree it's missing the last check?

Thanks for your help!

I work in accounting department and I reconciled all my 2021 check stubs. I’m sure they need to correct my W-2. 
I was hoping if anyone can guild me how to submit W-2C myself if they don’t want to initiate. 

@youme777

You can file a conventional paper return that includes IRS Form 4852 if all efforts to obtain a W-2 from your employer have failed. Here's how to fill one out:

1. Open your return and search for W-2. Select the Jump to link in the search results to get to the W-2 entry screen.
2. Fill out your W-2 as best you can using the information from your last pay stub.
3. Answer any questions until you get to the Let's check for uncommon situations screen.
4. Check the box next to Didn't get a W-2 and select Continue.
5. On the Let's check if you need a substitute W-2 screen, select Yes then Continue.
6. Answer the follow-up questions. Select Print to download and print your IRS Form 4852.

Returns including Form 4852 can't be e-filed per IRS regulations.

Use this link for more information:  About Form 4852

Only the employer can issue a corrected W-2 form  so your only option is to use the form 4852.  You could efile with the incorrect W-2  then once that return has completely processed you can amend the return and mail it in with the 4852 for the extra income.