Not gonna lie. I have converted several Kontakt instrumets to SFZ and DecentSampler by hand. It is time consuming (so pick one you really love).
If you have Kontakt 6, there is this LUA script that makes it easier:
First thing to do is to find an SFZ or DecentSampler instrument that is similar to the one you want to convert so you have a template.
Here is more info:
Using the LUA script:
The community thanks you!