Not a lot of usable data there, and, I‘m not 737 ‘spert, but sounds like a stuck pressurization outflow valve. They were probably to cheap to change it, opting to monkey around with it and see what happens. Could also have been a leaking door seal,
Red light…hmmm…not a friendly sign that. Cargo door not fully closed and locked? Red on annunciator could be several things as indicated in the link.
Amber - auto pressurization system fail.
Anyway here is a link to the annunciator panel cue cards for the 737-800.
Boeing 737-800 Annunciator Lights flashcards | Quizlet
Should be noted that repairing aircraft is done on the ground by engineers not by pilots in flight. Crew reaction was stupid IMO.