In K4 I entered a dropdown list with P1,P2,P3...P12. You mentioned using a dropdown list, so I assume you know how those work but I can give more detail if you need it.
Then in K5 I replace the date with this formula:
Formula:
=EDATE(DATE(2024,3,1),VALUE(MID($K$4,2,2))-1)
MID looks at the value in K4 starting with the second character. This has the effect of removing the "P" at the beginning. Then VALUE changes it from a string to a number. That represents the month number. The DATE gives the start of the first month, March 1, 2024. EDATE adds months to that. So we take the number after P, subtract 1, and add that many months to the starting month. This gives you the date in K5.
Since you had a date in K5 before, no other formulas needed to change, just the method for getting the date.
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