Hello @Greville0 Welcome to Air BNB. Your cottage looks very cozy. I believe the only way you can make the seasonal price changes is directly on your calendar. I manage my prices by frequently adjusting according to the traffic to my website.
BTW I notice you don't have a security deposit and I highly suggest you have one. Even great guests can have accidents and your compensation can be obtained through the Air BNB resolution center. I wish you much success with this business.