Perfect Past Achievement in Microsoft Solitaire Collection
Got Perfect in a prior month in Daily Challenges
How to unlock Perfect PastNote: If you completed all challenges in a prior month before this title update went live, there is a chance you can unlock this achievement retroactively. Go to Daily Challenges mode, pull up the calendar, and scroll back in time to the month you have a Perfect on. Load up any challenge from any day that month and complete it (obviously pick a quick Easy challenge). There is a chance that will automatically unlock this achievement. I completed a Perfect month in October 2017, and this didn't work for me, but there are reports of it working for others, so it's worth a shot before attempting to complete another month.
If this approach didn't work for you but you did already complete the base game achievements, obviously the next best thing is to choose one of the earlier months where you got a gold badge and start from there, completing the rest of the challenges that month. This is, of course, assuming that the month where you got the diamond badge is the same month you got the Perfect.
If you're starting from scratch, then refer to "Strive for Perfection" from the base list, as its requirements are the same (obviously make sure you complete a prior month and not the current month, though).