There are generally two ways you can set it up as an activity, and which is appropriate totally depends on the TV.
- you can put the TV into internet mode with a single button press
- the TV does not have to be on another particular input before the Internet button will work
- you are using discrete input selection (Method 2)
...then you can edit the device setup for the TV and add the Internet command as an additional input. Once that is done, just set up a new Watch TV activity but tell the Harmony software to use the new Internet input.
If any of the above conditions are not true, then you can still create a new Watch TV activity, with any existing input, then tack on the required Internet command(s) to the activity startup command list.
Here's an example showing where I have already added several custom commands to an activity startup and I could add another to my TV by clicking the ADD button: