My phone was bought from US Cellular, and I was able to use RCS then, but now that I've switched to Ting, RCS is gone from the settings bar. I did some searching and read that they do allow for RCS, but I just can't access it, and I don't know why. Both my app and software are up to date, so I don't know why this happened.
Close it out of the task manager a few times or go into settings - apps - messages and clear the cache and data from the storage section. RCS settings will eventually pop up, they can take a minute to get them but they should pop up eventually