Setting up a condition to verify if the 20th day of the month exist then do something, otherwise go to next workday

I have formulated workdays for a month and need to display in column next to those days data conditional to, for this instance:

if the day is the 20th , i.e : Day(Cell) = 20, do the thing on the 20th.

Some months though do not have a 20th, so i want the condition to evaluate if the 20th exist, else go to next workday and do what it was supposed to do on the 20th.

Current formula used is :

=IF(DAY(A16)=20;"do the thing on the 20th";"")

in the snapshot, April 2019 does not have a 20th of the month and therefore nothing is displayed in column C, i would want it to be displayed on the next workday which would be the 22nd of april.