Can we activate Scala 3 (dotty) on an existing Mill project manually?

I have used the "new project" option to experiment with Scala 3. Seems to work ok.
Now I have an existing project that uses Mill. Mill creates a IntelliJ project that allow
us to use the IDE. However, it it is for Scala 2.

Any way I can manually tweak the set-up to get the Scala 3 stuff?

TIA