If you have already been issued a short stay Schengenvisa (C-type) and you can’t enter the Netherlands under the current travel restrictions, the duration of your visa will not be extended.
The visa fees paid for issued visa’s that are not being used as a result of travel limitations are not being re-funded.
You will need to re-apply for a short stay visa. Due to Covid-19, all consular desks of Dutch embassies and Dutch consulates general are closed until April 6th. Depending on how the current situation develops, this period may be extended.
The appointment system to lodge an application for a short stay visa is closed and it is not possible to schedule any appointment for short stay visa until further notice.