Although it has been frequently requested, normal Roku functionality does not include a quick return to the last viewed channel app.
To switch between channels viewed within the Spectrum TV app, this function Spectrum would have to have built this capability into the Roku-compatible version of their app. I can find no mention of this capability on the Spectrum website.
It used to be the 'rewind' button to switch between 2 channels for Spectrum. Something changed and it's, now, the 'rewind' or 'instant replay' button.
