Can you not send a request to amend the dates for long term bookings? If so do that.
If not just extend the booking length on the platform, but you will lose the first seven days of your booking cost. @Mai1869
Yes of course you can cancel, but you will as you pointed out be liable for the entire booking cost.
I would make sure any payment you make is through the Airbnb platform. They can extend the booking and send you a special offer for the cost, but then obviously you would add the Airbnb fees on top of the cost you agreed with them.
It is not fair to ask the host to be out of pocket because you have changed your plans and want to move your dates, whatever your personal financial circumstances.