Check out pages 97 to 100 in the manual. Basically you will be creating hit transients of the kick drum and then creating a midi loop. How good it comes out depends on the audio. If there is a lot of bleed thru of the other instruments it may not perform this function to good. You can use an equalizer and maybe a gate to make the kick stand out more and subdue the bleed from the other instruments.
Do you have Melodyne that came with Mixcraft or an upgraded version. The upgraded versions can create midi from the kick drum track.
You can try to replace the kick drum with another sample with Melodyne, but I'm not sure you can do it with the version that comes with Mixcraft like in this video. I have an upgraded version.https://www.youtube.com/watch?v=n-2oZSeNBRA
There is an app called ApTrigga3 which will replace the kick drum with another sample but not midi. You can use the demo but after five minutes it starts to induce noise.http://apulsoft.ch/aptrigga3/
I do not know of any other free ways to do it.