First, make sure to detach the audio from the scene. If you don't do this you will not be able to edit the audio track.
To split or trim the audio clip, place the cursor where you want the split to occur and click the wave form on the timeline.
Select the "Split" option from the menu.
This will split the audio track in two parts. You can then manipulate each piece independently.
Here, we have split the audio file twice, to remove a section in the middle.
Click the middle clip and select "Remove."
Drag the other two clips back together.
You're all done!