On my TV box, I use a browser & go to any of the following sites:
(1) Box Asian --
http://boxasian.com/
(2) DramaCool --
http://dramacools.io/
(3) Drama Nice --
http://dramanices.com/
(4) Drama4U --
http://www.drama4u.org/
(5) HDFree --
http://hdfree.se/
(6) ICDrama --
http://icdrama.se/
(7) KissAsian --
http://kissasian.com/
(8) MyAsianTV --
http://myasiantv.se/
(9) NewAsianTV --
http://newasiantv.me/
(10) Viki --
https://www.viki.com/
(11) ViuAsian --
http://viuasian.com/
(12) WatchMe --
http://watchme.asia/
Plus many more sites !! (too many to list here)
Most above sites also have dramas from various other countries & also have movies (not just have Korean drama)
If a drama I want to watch can't be found in one particular Web site, I'll go to a 2nd (or 3rd) Web site to search & watch.
Of course you can go to the above sites to watch Korean drama either on your computer or on your TV box.
On computer, to visit any Web site, we use a browser (IE, Firefox, Chrome etc.)
Same on TV box, you just need a browser to go to any of above sites to watch drama -- most browsers will work.
Personally, I use a very (small size) simple browser app that you can get from Google Playstore:
https://play.google.com/store/apps/details?id=com.fevdev.nakedbrowser
Above browser app is only 120KB in size !! (yes, 120KB)
This small browser app is what I use on my TV box -- to allow me to watch (endless) various dramas/movies from most of the above listed sites.
I don't depend on apps like Viu to watch Korean drama.
Hope the above helps.