Echo is not officially A device that smartthings can control: it is an integration where voice instructions to echo can be used to control smartthings-connected devices. That’s very different than, say, Sonos.
As @orangebucket mentioned, there are some custom projects which do you allow you to have more control over echo as a device, but they are fairly complex to set up.
A simpler method is to hook into the existing echo routines (not smart things routines) and trigger those based on logic on the SmartThings side. It’s not as powerful as echo speaks, but it’s a very popular method for use cases like getting echo to speak a particular phrase when something happens or playing specific music based on a smartthings trigger.
I don’t know if that would match what you were looking for, but here’s the FAQ:
(The topic title is a clickable link)