How to make/edit a battle animation?

In my hack, I want Valkyries to wield swords, but, even though there were troubadour w/ sword animations, there wasn’t any for the Valkyrie. I was originally thinking of asking someone to make one, but I figured it would be cheaper to learn how to make my own. So how do I do it? I haven’t seen anyone make a guide for making battle animations, and I would appreciate it if someone could explain it to me.

As far as I’m aware, it’s simply a matter of artistic ability, work, and technical understanding of how animations work (i.e. number of frames). Consider looking at existing animations and seeing how they work and you can make a basis off of that.