Something like this should work if you have everything set upright
"Alexa, Tell Anymote, to change the TV input to HDMI 1"... or 2 or 3... whatever...
This seems like the same item as the harmony Hub I use, and works almost the same... except I ask Alexa to tell Harmony to do whatever I need done...
In your case,"Alexa, Tell Anymote to ___________" is the key to getting it to control through Alexa and Echo products. You definitely need to address whether your smart TV and everything is set up properly... but once it's set up... pretty simple. Just have to figure out the commands to use.