The K20 plus is a rather low end phone. It simple doesn't support things like HDMI over USB, or USB on the go. You can try an adapter, but I'm telling you now from what I know of that phone it simply doesn't support HDMI.
Assuming you are trying to play something from your phone on your TV, try casting. I'm not sure if that phone supports it, so you might need to buy a chromecast or other such device. I personally had bad luck with it but you might do better.