You can build a lookup table in an unused area of the worksheet or in a separate worksheet. Column 1 of the table would contain the days of the month (in order) and column 2 would contain the event(s) that should occur on that day. For sake of demonstration, put this table is Q1:R31
If cells A1:A31 of your calendar contain the dates of the month then cell B1 would contain =VLOOKUP(DAY(A1),Q1:R31,2,FALSE) and you copy this formula to B2:B31.
You many need some extra processing for events that occur after the 28th.
However, since the 10th of the month will always fall in cell A10, the event for the 10th will always fall in B10. So I wonder why you need this at all.