You can find the autosplitter under Resources.

Setup:

1. Download the Autosplitter
2. Extract it into the components folder of Livesplit
3. Go to Edit Layout
4. Click on the plus and add "Scriptable Auto Splitter"
5. in the Layout Settings of "Scriptable Auto Splitter" click on browse and select the ASL
6. After that make sure you that you are comparing to game time by right-clicking on Livesplit and under "Compare Against" the last 2 options select "Game Time"
7. THE AUTOSPLITTER ONLY WORKS IF YOU HAVE 3 SPLITS