Without the model number of the TV we can only guess what connections it might have.
Option 1 If the TV has a headphone jack then connect that to the aux input of the soundbar.
Option 2 is to connect your source that is now connected to the HDMI input of the TV to the HDMI input of the soundbar. Connect the HDMI output of the soundbar to the HDMI input on the TV. You can add an HDMI input selector to expand the number of HDMI inputs.
Option 3 would require you to open the TV and connect the wires that now go to the internal TV speakers to a speaker to line level converter. That would provide an analog audio output for the aux input of the soundbar.