What's the best way to setup animations for an anim montage?

In the UE4 3rd person tutorials there were animations for a left punch start, right punch start, left punch end, and right punch end. They needed these start and ends to blend between interruptions. I want to do this for a sword animation I have.

What’s the basic method for splitting the animation for this?

Would I want to split my sword animation in half and then reverse it?

Is there any easy tool that can split existing animations on a timeline?

Do I just need to use an animation program to export specific frames?

Any input would be greatly appreicated and helpful for others.

Thanks