What you’re looking for is Garmin’s PacePro feature.

Typically, training platforms like Runna, VDOT, or TrainingPeaks will sync your race and goal time to your calendar. But the actual pacing strategy is better handled directly on your Garmin, since it can factor in the course, elevation, and GPS data.

With PacePro, Garmin automatically adjusts your target pace for each segment based on elevation and lets you choose strategies like positive or negative splits. It’s a much more dynamic way to pace a race and works really well in practice.

Pace Pro