I have no experience of optical audio however I would :-
Look in the manual.
Look for a manual on google.
(Take some care for dodgy software. DON'T download software. Look at it in your browser or download PDF. If unsure post details here.)
Post EXACT Model number here. Usually in middle of back panel. I usually photograph it and transcribe at leisure.
e.g. I have a Toshiba "Model No. 32XV635D" here.
It also says elsewhere "32XV635DB", more is usually better. I suspect "B" is a country code.