You can select a range of dates on your calendar, select Edit, and then change the Pricing. The new price will be applied to that range.
Another way to do it is to set up a rule-set to reduce your price a certain percentage during your off-season, and then apply that ruleset to your range of off-season dates.
I’m not aware of a way to do it that is more “automatic” than this, but it only takes me 5-10 minutes a year to set my high/low/shoulder season prices for the year using the first method above.