you seek to feed the audio line output to the input of your audio amplifier. enter the model numbers into your search engine to seek the manuals or if it is easier, examine your devices carefully with a flashlight. for inputs, outputs, and model numbers. some jacks may be hiding on the rear or side or both or front cover of the tv.
this example presumes you are feeding cable box but not hdmi: instead of sending the red and white audio rca output to the tv, send it instead to the input of the audio amplifier.