Hi jsakura7, thanks for speedy reply. Really appreciated. I was trying to find the Content Share icon on my Samsung A12 as this is what was requested on LG TV, but I gave up. Maybe its not available on my phone!
I messed about with RTE player app on phone and yes I can see the above icon / image but I ended up having to plug in a very old Chromecast to HDMI slot on back of TV and charge via the USB cable provided. Then I downloaded the Google Home app to manage the Chromecast. Managed to get it to work and can now cast RTE player to LG TV screen.