Because the 2023 RMD was not taken in 2023, it is not 2023 income and did not add to your taxable income on line 15 of your 2023 Form 1040. Therefore, no income tax would have been paid on this amount with your 2023 tax return. However, unless you requested a waiver of the penalty when you originally filed your 2023 tax return, your 2023 tax return would have included an excess-accumulation penalty, shown on line 55 of your 2023 Form 5329. (It seems that you did not request such a waiver.) That's an excise tax, not an income tax. To receive a refund of that excise tax you would have to file an amended 2023 tax return (Form 1040-X) along with an amended Form 5329 Part IX and provide explanation with reasonable cause to grant the waiver. If the waiver is granted, the IRS would refund the excise tax that you paid when originally filing your 2023 tax return. If the waiver is denied, there would be no refund. The IRS instructions for Form 5329 Part IX indicate how to request the waiver: https://www.irs.gov/pub/irs-prior/i5329--2023.pdf
As others have said, the 2024 Form 1099-R is simply reported on your 2024 tax return, adding you your 2024 taxable come and your 2024 tax liability.
