If you use the code which is linked to in the community FAQ, then you will end up with a virtual device which is both a sensor and a switch.
Turning the switch part on will make the sensor part look like it is open.
Turning the switch part off will make the sensor part look like it is closed.
So you will be able to trigger the echo routine from the sensor part being open by having a smartthings automation turn the switch part on.
But an echo routine cannot set a sensor to closed. So you would have to use the name of the device which is the switch name if you want the echo routine to change it.
That means that when you look at an echo routine, the sensor name should show up As an option under the IF and the switch name should show up as an option under the THAT.
Is that what you were asking? I found it a little bit confusing.
But you have to be using the code from the FAQ or something similar so that your one virtual device looks like two devices, both a sensor and a switch.
FAQ: Can I trigger an Echo Action without Speaking to It?
If you can post a screenshot of your automations, that would help. 