Urgently Need help: 2018 Excess Employer contribution self-correction

Hi,

I have a sole proprietorship PLLC business.  For the year 2018, my CPA incorrectly calculated Maximum Deductible Employer Contribution to my solo 401k, which was contributed in April 2019.  I found out in May 2020 that it was over by $687.  I self-prepared by 2019 taxes in May 2020, and I correctly calculated  Maximum Deductible Employer Contribution $9554.  In the recent call with the CPA, he says this qualifies as "self-correction" with recommendation to reduce 2019 contribution from $9554 by $687 (excess employer contrib for year 2018) BEFORE July 15, 2020.  $9554 has been kept as cash till date.  He says I need not file any forms etc i.e. no Form 5330 needed.  

Questions:

1. Is it correct that I need not file Form 5330? 

2. What are the consequences of not filing Form 5330 if I am expected to by the IRS? 

3. If I should file Form 5330 and the CPA is not supporting but I still file, am I dead in water if there are issues?  Against CPA advice me filing Form 5330 ensures that he certainly won't cover the fees and taxes associated with his mistake...  

How would you proceed if you were me?  I need to remove $687 ASAP from e-Trade to be effectively out of the account before July 15th and avoid further issues.

Please help!

Thanks a bunch!

Amend your 2018 tax return reducing your employer contribution deduction by $687 (that was over contributed in April 2019)

Treat the $687 as an employer contribution in 2019.

53 minutes ago, Lou S. said:

Amend your 2018 tax return reducing your employer contribution deduction by $687 (that was over contributed in April 2019)

Treat the $687 as an employer contribution in 2019.

This.

And then hire a professional TPA to do all your 401(k) compliance work.

Thanks