Open Kontakt 5 using the cog icon on the track, load in an instrument and change the Kontakt tracks channel to Port A => 3 (slot 3 as set in step #2) or whatever slot you used in the Sibelius mixer. With Sibelius First you can start composing music using the same tools professional composers use.
Let's say I change the Flute I to "slot 3" (this basically means Channel 3 of the active VST) using the small green up arrows: Now you can change the slots in the mixer from 1 to 16, but make sure Kontakt 5 is activate for that track. Complete layout control Sibelius 5 also offers users complete and easy layout control, covering bar and page numbering, blank pages, sheet music margins and more making it easier than ever to produce beautiful scores. Sibelius gives you two options when entering into percussion staves with a MIDI keyboard. Easy instrument change: Sibelius automatically transposes the music and changes the sound used for playback. There are many different drum maps in Sibelius and the sounds and noteheads are frequently assigned differently in each map.
If the checkbox for "use manual sound sets" isn't checked and the number of channels is not set then you won't be able to change the slots in the mixer. Sibelius uses percussion maps or drum maps that assign sounds and percussion notation to specific lines and spaces. Make sure Kontakt 5 has the "Sound Set" set to "(none)" (As shown in your image already) then go to the "Manual Sound Sets" (the next tab) and check the box labelled "Use manual sound set" (see image below) and the No. Anyway, a few things need to be done first before Kontakt will work properly. Not only can you respell notes this way, you can also change a note to any. Not reviewed in the tutorial is a more advanced one that will handle situations if the encoder skips MIDI PORTS.
Not sure if you've managed to work this out yet. The Sibelius Sounds library which ships with Sibelius 7 and later does not.