Disclaimer: Boring Video.
Everytime I turned on my spectrum app on roku.. it default to channel one
It's actually easy to change this setting so it opens up a different channel.. or at least turn it off.
Press the back button at the top left of your roku remote to turn on the top menu nav buttons.
Then move up until you are actually on the menu... and go right until you're over the Gear Icon (settings).
Click on that.. ant the first screen for preferences will show how to change or turn off the default loading channel.