You can find the most actual and available bus timetables here:https://www.e-ktel.com/en/services/dromologia
You should be able to book tickets from there too.
You need to take the bus from Heraklion West bus station towards Chania, and then indeed, when passing Vrisses, change bus, to the Chania - Chora Sfakion one, also crossing Vrisses. Please note at what time the last bus of the day from Chania to Chora Sfakion is passing Vrisses. That is the last moment you can make the connection from Heraklion. In early season this last connection time is often at 14:00 hrs. That means that you need to be in the bus in Heraklion at the latest at 11:30 AM, to make it to Chora Sfakion in the same day.
Somewhere in summer there will be a later connection. If, and when? In these pandemic times nothing is sure. So please keep following the above page nearer the time you need to travel, to look for changes.
BTW, it is also possible, much faster but also more expensive, to make the trip by taxi, directly from Heraklion airport to Skaloti. It takes about 2 hours, instead over 4.5 by bus, and will cost about € 150 one way.
To book a taxi, ask your host in Skaloti, or book online with the Sfakia Taxi Company:https://www.taxi-sfakia.com/
Have a good trip!
All the best,