Single Member 401(k) - Excess Contribution Solution

I have read so much I am now becoming confused..... here is the situation -

A CPA reached out to me regarding a single member client she has.  This client was persuaded to open a 401(k) by the financial advisor who quite frankly I don't think knew anything about pension plans.  Anyway, here is what happened:

She opened a 401(k) for 2020
Rolled SEP money in (lots)
Contributed to the plan in 2020
- Deferred the max (23K)
- Maxed the employer (37.5K) upon advise of the financial advisor
ONLY HAD $35,212 in schedule C compensation

All contributions made in 2020.  

Taking the excess contribution out starts with deferral money then employer? or does it matter?

Depending on what comes out.... 
1099-R the deferral... withhold taxes
1099-R the employer, don't withhold taxes, code 8P
perform the withdrawals before the 2020 taxes are filed

Thanks

Since first year, is there ability (and support in plan document) to pull out excess employer contribution that is not deductible, either on mistake of fact (insufficient compensation) or on the failed contingency that it is deductible? Not sure if/how this works if tax return has already been filed with the excessive deductions.