Hello @Kim-And-Ann-Sophie0,
You can't unblock the dates. Blocked dates are one of the penalties for cancelliing.
I’m a host. What penalties apply if I need to cancel a reservation?
You have instant book so I'd contact Airbnb support to discuss the circumstances with them.
Type "contact airbnb" in the "Search the community" box on these forum pages where you posted your question. Scroll down a little in the list of suggestions that appears and click on the "Contact Airbnb: A Community Help Guide[UPDATED]" one. That lists phone numbers and ways to contact them via Twitter or Facebook.
Steve.