How do you write April 9?

A: IV・IX・MMXXI Your question is, What is April 9, 2021 in Roman Numerals?, the answer is IV・IX・MMXXI.

How do you write June 2019?

Do not abbreviate days of the week. March, April, May, June and July are never abbreviated in text, but the remaining months are when they are followed by a date (Jan. 27), and are correctly abbreviated Jan., Feb., Aug., Sept., Oct., Nov., Dec.