I would approach it this way:
Get the variable in the row which is the date you want checked, then turn it into a DateTime variable (either Parse date, or CDate), then you could check if the dd part = 01.
Here is how:
Use a For each row loop and inside that, use a Get row Item to retrieve the correct column in each row that contains your date variable.
Call the row date something like: DateVar (genericvalue type variable will work fine)
Then in an assign do this code: DateVar = CDate(DateVar).ToString(“dd-MM-yyyy”)
Then an IF statement: DateVar.ToString.SubString(0,2)=“01”
THEN: Add message box “this is the first of the month” <- can do anything here you want really, message box was used as example only.
ELSE: add message box “this is not the first of the month”