Turn your soundbar on .. then goto the settings on your TV and navigated to sound setup. From there you should be able to choose your sound set up. Have your sound bar volume turned up as you can always turn it down once you have it working.
OMG I've been faffing around with this thing for 2 days now and it's driving me round the bend ... can't connect my TV to it via WiFi. Can't get Alexa to work ... I've uninstall, reinstalled, turned off, turned on, reset router, deregistered Alexa device, re-registered, absolutely fed up and returning it 😩😩