Right now, you must apply for a new visa, and it doesn’t look like fees are refunded or waived:
Is a visa fee refundable?
Visa fees for visas that have not been used by COVID-19 cannot be refunded. A new application must be submitted.I have not travelled to the Netherlands yet. Can the period of my already issued visa be extended?
The duration of issued visas of travelers who have not yet been able to travel to the Netherlands due to cancelled flights cannot be extended. A new visa application must be submitted.
Whether this changes in due course is something no one knows right now.
Credit:stackoverflow.com‘