Need an RCA sound bar RTS7010B code for RC73 remote. Receiver is HR54-200.

You should be able to simply rerun Remote Setup via the Settings submenu on the HR54-200. Program it for Speaker or Soundbar (can't recall what it is listed as) and select RCA. The receiver will either manually find a code and program the remote for you to control the sound bar or you will have to enter the code yourself and the receiver will give you a list of possible codes as well as the steps required. Just follow the simple steps and you should be good. 

I’m able to find the RCA sound bar model number in the audio list.  The receiver says that the code is received, but when I test the code, the sound bar does not power off.  I’ve also tried different model codes, but they didn’t work either.  Is there any other way to add the sound bar?  The DirectTV installer had a hard time finding the right code, but he did eventually, not sure how.

@Bijjjoux2021 you may have to try other codes for that specific soundbar model if the first on the list does not work. If the receiver itself fails to program the soundbar correctly manually (meaning it doesn't give you the option to do it yourself) you need to perform it manually by looking for codes online for the RCA soundbar.