What is the most logical next event?

How to prevent a car from rolling back on a hill
Come to a complete stop.
When you are on a slope, you need to come to a complete stop using either the brake pedal or the handbrake. This holds true whether you're facing up a slope or down a slope.
Some drivers prefer to use the handbrake, because it frees up their right foot to use on the gas pedal when they intend to start driving again. Use hill-start assist, if available.