Hello Raffi 1305
I had the same problem at the beginning.
After a long search on the net, I found an almost embarrassingly simple solution.
Switch everything off and disconnect it from the mains (TV and soundbar). Make sure that the ARC-HDMI cable is connected to the correct socket.
Switch everything on and off in the same order. First the Soundbar, then the TV.
The TV checks all IN/Outputs and should recognise everything.
I hope it works for you.
Greetings Hohenheim