Hi, tried asking SQ but very long wait at the call centre!

1. Can I cancel and get refund for partially used award ticket (J - Saver)? I book a return ticket but flew the departure flight and would like to cancel the return flight.
2. I know Singapore is strict about covid, I have a cough but negative self antigen test, however I am worried I wont be allowed to board or other passengers in J (business) may protest, should I be worried? This is the reason of my question #1, if the pax and flight crews are cool with cough then I can fly the return award flight. My destination country does not require any covid test, I am triple vaccinated.

Many thanks