The easiest method would be to make a variable that evaulates as an expression. Your variable expression should look like this

"/out/export/" + RIGHT("0" + (DT_WSTR,2) datepart("d",Dateadd("dd", -1, GETDATE())),2)

Then in the connection string expression just call the variable.

This will always produce errors because you are providing to many parameters for datepart. The datepart parameters are (datepart,date). I think you are tying to use dateadd which requires three parameters (interval,numer, date).

I resolved what I believe you were trying to accomplish in the code block above.