Retirement tax questions

Related question: I didn't take my RMD for 2018 until Sept. 2019. (I am 73.) I already filed my 1040 for 2018 in early 2019.  Do I now file a form 5329 for the year 2018? And do I mail it to the IRS alone, or should I attach it to my 1040 for the year 2019?