Thanks for replies, particularly to ColinS for such a detailed and helpful reply. On the interior lights, there are just the two push panels to switch the left or right lights on or off. Where I would expect to see a sliding switch to switch the lights to auto mode as on previous Accords that I have owned. the opening is filled by a small perforated panel only.
I will attempt to remove this to see what is behind. From observation, it would look as if a sliding switch has been removed and replaced by a cosmetic panel of similar size.
This reads as if you are not aware that there are two interior light fittings. You seem to be referring to the unit above the windscreen, which contains the "Map Lights" mentioned by Trebor1652. I think the perforated panel conceals the bluetooth microphone. I wouldn't recommend digging that out to look for a switch that isn't there.
ColinS is referring to the other light unit in the ceiling panel. This is the one that has the sliding switch.
If still puzzled, you might find pages 194-195 of the handbook illuminating (sorry, couldn't resist that !)
Edit: just realised you have a 2018 model, so the page numbers in the manual might be different.