We forgot to take an RMD for 2017 from wife's IRA, so took it 1/2/18. I know I'll have to request a waiver of penalty. Do I do that for 2017 or 2018 return?

We took a late RMD from my wife's IRA on Jan 2, 2018. For that same account I had to report a rollover to a different institution. When I filled in the rollover distribution I couldn't figure how to report the late RMD so that I could request a waiver of penalty. Since the RMD distribution was in 2018 do I report the late RMD on 2018 return or does that need to be reported on 2017 tax return?