I have used a simple DAW before and there was a trim function where I placed the timeline where I wished to cut it and pushed a button. Is there anything like this in LMMS?
The LMMS manual says on page 43
Note that an entire element always gets deleted as a single unit (you cannot selectively snip away parts of an element – You will have to edit the contents of the element, as described below.).
and on page 47
LMMS cannot edit this track at all (e.g. trimming/slicing, or scaling it to fit with the bars in your music). You have to edit the track beforehand, using an audio editor (e.g. Audacity).