apt-get unable to locate packages

[okir]

Just got my pinebook 11.6 (1080p) a couple days ago.  Overall I am pleased with it but am having some issues with apt-get.  I am still running KDE neon which came on the pinebook.  I add repository key - get the OK response, then apt-get update -this seems to go like normal, but when I try to apt-get install <package> i get 'E: unable to locate package  <package>' I'm fairly new to linux in general and am really stuck on this issue.  I've tried sudo apt-add-repository multiverse  etc but am still getting the same error unable to locate package.  Should I try to flash a different os?  or am i missing something simple here?  I'd really appreciate any help with this.
Thanks!