@Taff0
Airbnb collects payment for long term stays monthly and pays the host monthly. So, if you intend to honour this stay and receive the payments via Airbnb, snooze the listing (or go to the calendar and block the dates) rather than delete it.
Or, if you are determined to delete the listing, you will need to figure out a way for the guest to pay you direct and be sure you trust them to do so.
Do not cancel the stay from your end as you will be fined and that will probably be quite hefty given it's such a long stay. If the guest cancels, they will also lose the payment for the first month as per the long term cancellation policy. So, if you want to take this off the Airbnb platform, and trust the guest to pay you, you need to do an alteration request to bring forward the check out date. Make sure that you receive the payment from Airbnb for the amount the guest is not due back. Then you can delete the listing.
However, it does seem much easier to snooze it. I don't know if that effects current bookings or not though as I've never tried it.