Barbarian features not appearing for prerequisite class feature option

Im trying to make a barbarian subclass and have a feature that gives extra resistances when rage is activated but i cannot find how to choose the activate rage prerequisite option

Quote from NoodleDoots >>

Im trying to make a barbarian subclass and have a feature that gives extra resistances when rage is activated but i cannot find how to choose the activate rage prerequisite option

 
There is no way to do this.

You can create a separate toggle-able thing they would need to activate manually, and separately, when they range. See the Homebrew FAQ pinned in this forum for how to do this.

Homebrew Subclasses & Races Species FAQ > 2. How do I create a temporary/activated effect that only applies to the character sheet when turned on, and only until turned off again?