When you amend the return, you will remove the DCFSA and the amount ($5000?) will be added back to your taxable income. However, you should be eligible for a revised dependent care credit that will cover some of the difference. Since the credit is 20% of expenses and your income tax rate might be 22%, 24% or higher, the credit probably won't cover all the taxes on the added income. After filing the amended tax return and paying the additional amount owed, you may get a bill for interest back-dated to the original due date of the return, April 18, 2023. This is unavoidable and can't be waived. (However, per Mike, you could make an argument that your employer should reimburse you for the interest.) If you owe more than $1000 in additional tax, the IRS could also include penalties for under-paying your taxes, also back-dated to April 18, 2023. This penalty can be appealed for cause (and you have a very good cause).
You will also need to file an amended state tax return.
[Edited to add: You should probably expect to get a corrected W-2 from the employer. Wait for that to file the amended return.]
