Add days to a date item

Hello :-),
i have saved a date in a date item. Now i’ll add a specified number of days to this saved date. How can i do that?

I have tried this, but this does not work:

val Aufgabe12_Datum_format = (Date_Aufgabe12.state as DateTimeType).getZonedDateTime
Date_Aufgabe12.postUpdate(Aufgabe12_Datum_format.plusDays(30))

thanks!!

André

Try

Date_Aufgabe12.postUpdate(Aufgabe12_Datum_format.plusDays(30).toString)

Thanks! That worked!