Sample Harmony activity to turn TV volume up one.
Here the TV is listed three times in the “Louder 1” Activity Start Sequence. Once to power on, once to NOT change the input, and once for the volume up key
Here I am setting the device to NOT change the input channel.
And selecting the VolumeUp key as a step in the start sequence. Choose Edit Entertainment Device, then the device, then the command. (This is also how you could choose a starting channel)
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The end sequence just powers off the master device. This means it will not turn off if I’m changing to any other activity that also uses the TV.
add a second activity that does the same thing so you can switch between them
Then I make a second activity that does exactly the same thing, it just has a different name.
Again, make sure you have the activity working the way you want on the Harmony side from both the Harmony app and the button remote before you add the echo trigger in IFTTT. 
And as I said, I think control of volume is way too much work for most able-bodied people, both to set up and to use every day . But for those with limited hand control, it’s very useful.
Adding a specific channel to the start sequence
Setting up a starting channel is work to set up, but very easy to use. It just becomes “Alexa, trigger Disney channel” or “Alexa, trigger ESPN TV” or “Alexa, trigger Netflix” or whatever. So I think a lot of people like those. It’s just a matter of setting a starting channel for the activity. But you will have one activity for every favorite channel. And one IFTTT recipe for every activity. So that’s why you have so much set up work.