I used a 3.5mm female to 2 RCA male adapter. The audio output is great, but now I can’t control the volume using the TV remote, which is very frustrating. 
Most 3.5mm female-to-male RCA stereo audio Y-lines have no volume adjustment function. It is worth noting that most of the products on the market do not support it. However, some specially designed 3.5mm female-to-male RCA stereo audio Y-lines may include a volume adjustment function. These cables typically have an additional knob or control switch on the 3.5mm plug to adjust the volume. This type of cable is relatively rare and is usually a specially designed-product.
what model of device you are using?
I just tried connecting my Samsung plasma tv to a bluetooth soundbar
I guess there’s no way to adjust the volume with the remote control. 
Have you tried to reset the smart hub?
Click Settings on your remote and scroll down to Support > Self Diagnosis > Reset Smart Hub. Enter the TV’s PIN (default PIN is “0000”).