How do I use a third-party speaker to disable only one of multiple connected devices of the same type?

Set different names for these devices and use voice commands to control them.

For example, name the lamp in the living room as "living room light" and that in the bedroom as "bedroom light". Then, tell your Alexa Echo speaker "Alexa, turn off the living room light" or "Alexa, turn off the bedroom light" to turn off the lamp.

This method also applies to Tmall Genie.