I'll be shocked if you can get this resolved by 4/15.  Either way, the excess contribution goes on the 2023 1040 Line 1h.  If corrected after 4/15 it gets taxed AGAIN in the year of distribution.  NerdWallet has a good "plain language" article that I've used to have the client send to their plan administrator when the admins seem to be clueless:

https://www.nerdwallet.com/article/investing/excess-401k-contribution-what-to-do

BTW, contrary to what the article says, I've NEVER seen a corrected W-2 when this happens.  If you do get a corrected W-2 then you'll increase Line 1a and have nothing in Line 1h.

You're not going to get any traction with Fidelity.  It's the employer's plan so the employer has to initiate the correction.  For whatever reason this seems to take weeks/months and a series of follow-ups.  Recently there seems to be a lot of push-back by the big retirement companies.  The last one I had never did get the correction done, she finally gave up and 4/15 passed so she'll pay tax on that income twice.

I have one this year that's in progress.  I've pestered my client three times about it, "hey, get this done ASAP because it can take a while" but nothing yet (I don't know if it's the client or the employer that's dragging feet).

I've seen on other lists where tax practitioners have a Jan/Feb email that goes out to everyone reminding them to check their W-2s for excess retirement contributions.  I may adopt that next year.  Seems like I have at least one of these each year and it's always a nightmare (and I don't have that many clients!)

Rick