I think many FL Studio users here. So here is how you tune the kick.

1. Open the kick sample in Edison. You can r-click sample in sampler - edit.

2. In Edison with the Regions button(5th button from the left, after scissors and wrench) choose - detect pitch regions. It can do the job or it may fail. Depends on the kick type. Often it will do.

3. Go back to sampler. Click INS or other tab so you see keyboard. And then right click the note that Edison showed you(if you don't know notes google for Keyboard Notes). So now your kick attached to correct keyboard notes. The G note will be G. You can choose the note you want your kick to be tuned to.

4. You can pitch up the kick +24 and listen how its note sounds with the song. It can help you to hear the tune of the kick and fine tune it.

5. Choose the note of the kick to be relative to your main bass note. You better to stick with D-A 37-55hz notes range. So if your bass is out of this range then just +7 +5 or -5 the kick's pitch. This will work too like the 5th types of leads.

This is very very important your kick to be tuned with the bass. So learn to do that!