Is this the back of your TV?
If it is, read what it states below and above the L/R RCA audio plugs. Those connections are for INPUTS not OUTPUT of audio. Since you got a cheap soundbar that does not have an optical input, you need to get an optical to RCA converter like this
https/www.amazon.com/dp/B00KNNSKV0?psc=1
A better idea would be to return this Axess and get a better quality soundbar with the correct inputs available. The one you got has some pretty bad reviews for sound quality, a descent one would be may be $30 more which is time and money you would spend on getting an adapter in the first place.