Hi there @Nanda_Rukmana,
to add my solution as well (similar to one @ScottF provided already). I decided to use Column Expressions node to determine the first day of previous month.
https://kni.me/w/-KYIGjuZiK3HAOOF
Additionally this seems as a frequent request. Not exactly this one but some kind of date creation/manipulation based on execution point in time. Hopefully we will figure out a way to make this easier in KNIME. Or someone maybe willing to create a Component? 
Br,
Ivan