Simply repeat the name of your ecobee. If Alexa still isn’t sure which device you meant, it might mean she isn’t able to understand the name of your ecobee. Here are a few things you can do:
Make sure you’re using your ecobee’s name correctly. To confirm what you’ve named your ecobee, on your thermostat, go to Settings > Preferences > Thermostat.
Make sure that your ecobee’s name is easy to understand. For instance, Alexa will have trouble understanding ‘ecobee3 lite’ or a name that is spelled differently (such as 'b3dr00m').
You can change the name of your ecobee at any time by going to Settings > Preferences > Thermostat > Input the new name. Once you’ve changed it, you’ll need to ask Alexa to discover devices again.