If you use Auto mode, you can still ask Alexa to change the temperature by saying, “Alexa, set [Thermostat Name] to [number] degrees”. Alexa will respond to you by saying, “Thermostat in Auto Mode. Aiming for [number] degrees.” Your ecobee will then use this temperature as the midpoint between your heat and cool set points (based on what you’ve set your minimum heat and cool temperature to).
For example, if you’re in Auto Mode and you ask Alexa to set the temperature to 72F (22C) and you have your minimum heat/cool temperature difference set to 5F (2.8C), your heat set point will become 70F (21C) and your cool set point will become 75F (24C).
To check your minimum heat/cool temperature difference in Auto Mode, go to MENU > SETTINGS > INSTALLATION SETTINGS > THRESHOLDS > HEAT/COOL MIN DELTA