401k excess salary deferral in 2020 but missed Apr 15 deadline

I changed employers in 2020 and accidentally exceeded the 401k contribution limit. I did not realize this until after the Apr 15 deadline. I have contacted my employer's benefit provider and they have initiated the process to withdraw the excess, but have informed me that it will not likely be completed by the May 17 filing deadline. I know the amount of the excess contribution, but not the amount of the earnings on it. Do I need to file an extension for both my Federal and State (CA) returns or is there a way to correctly complete my returns by the filing deadline? Once the withdrawal is complete, what is the correct process to follow for my 2020 returns? I understand I will get a 1099-R to report the withdrawal on my 2021 returns, which seems fairly straightforward.

 

Thank you!

John