You can setup auto-update of Scala plugin Nightly builds in IntelliJ IDEA in the Preferences menu under Preferences | Languages & Frameworks | Scala | Updates

Select the Nightly Builds update channel from the drop-down menu:

Or if you cannot do it from plugin settings If this does not work, add "https://plugins.jetbrains.com/plugins/nightly/1347" to custom repositories under

Preferences | Plugins -> Gear icon -> Manage Plugin repositories: