Model numbers would help.
If your LG BD player only has HDMI out then you have two options.
1. Connect the RCA to your TV directly then you will get sound on the BD player if it is connected to the TV.
2. If the BD player only has HDMI out then you would need an audio extractor like this one http/www.amazon.com/ViewHD-Extractor-Support-Converter-VHD-H2HARC/dp/B00LKF6CPG