select start and stop dates for the calendar OR extend existing calendar into the future

I've used HebCal for quite a while. Every few years I want to extend it into the future. (I don't what to have it go on infinitum.) I was trying to get a fresh update for 2021 - 2023 today. Unfortunately all I could get was 2020-2021. Since I already have 2020 in my calendar I ended up with double entries for the entire year. I need to start on January 2021. I thought there was a way to do this in the past, but I don't see a way to do it in the current version. I'm using macOS.