Personal definitions aside, these two things are essential. Heroes stand up for others. Heroes take action when no one else will... This villain is called Someone Else Will Do It...
You won't, in the moment. You won't want to. It will be overwhelming. But you can force yourself to act anyway.
And you can train. You can make yourself ready to overcome the bystander effect.
This is the dirty little secret of heroes. They're not special, not chosen by prophesy, not irradiated or born with powers. They work at it. It takes a willingness to challenge yourself, and a heroic imagination. You can cultivate these traits.