Open Garage, then Engine. Set your engine type, maximum RPM, the distance between services, and the two shift light thresholds: RPM warning, which displays orange, and RPM critical, which displays red.

Set these to your engine, not to the default. A stock default on a built engine means the red light arrives after the point you needed to shift, which makes the shift light decorative rather than useful.

How to set them:

1. Press ENGINE in the Garage menu.
2. Set the engine type and maximum RPM for your build.
3. Tap RPM warning and set the orange threshold.
4. Tap RPM critical and set the red threshold.
5. Set the distance between services if you want service reminders.

A common starting point is warning around 500 rpm before your shift point and critical at the shift point itself, then adjust after a session.

Related: How to Set Up the RPM Shift Blinker · Gear Setup: Entering Ratios or Calibrating Gears · How to Open the Garage Menu