how can i get tcl roku to play sound thru me home theatre system?

Without makes and model number we can't give you an exact answer.
In general you would connect the audio output of the TV to the audio input of the HTS.
Options for doing this would be
optical or coax digital audio
headphone or analog audio
If you don't have matching TV out to HTS in you will need a converter.
Check the TV manual on how to turn use the audio output. You may need to turn it on, turn the TV speakers off, and change the audio output type in the TV menu.
This is to get audio from the TV to the HTS not get video from the HTS to the TV, Only the HDMI-ARC connection would accomplish both. You would need to have ARC in both the TV and HTS to get that to work.

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