First of all, you weren't taxed on the deferral on your W2. This was treated as a tax free contribution, or should been treated as a tax free contribution.  Contrary to your belief, you weren't taxed on this contribution.

Next, you need to tell the trustee that you need to withdraw this from your 401K. The IRS mentions this in this publication. This withdrawal request must be done before April 15.  

Next since the amount isn't taxable, we must report the withdrawal as taxable compensation.  To report this:

1.  Go to income
2. Less Common income
3. Miscellaneous income 
4. other income not reported on a W2 ( This may have been reported but not treated as income).

Next year, you will receive a 1099R that reports the excess contribution withdrawal. The 1099r will not be taxable income to you however because of the codes that will be given in Box 7 of the 1099R form.

Please read the link provided for further details.

Consequences to a participant who makes excess deferrals to a 401(k) plan

[Edited 03/25/25|11:15 am PST]