If you are past your beginning year and missed your RMD, you must file form 5329 to report the missed RMD and pay the penalty. (The April 15 grace period is only allowed in your beginning year.) However, you can request a waiver which is almost always granted. You should take your 2023 RMD as soon as you can (it sounds like you already did this)? Because it was taken in 2024, it will be taxable next year, not on your 2023 return. But don't forget to also take your 2024 RMD before the end of the year, because the January 2024 withdrawal is counted for 2023.
If 2023 is your beginning year, then you are not late, because you did have until April 15 of the next year. Just report the income on your 2024 return as normal. Don't report a missed 2023 RMD. And don't forget to take your 2024 RMD before the end of the year, since the January 2024 withdrawal is counted for 2023 even though you had a grace period.
