You open any animation with what you want in any DCC and you copy the curves over to your file - each dcc does it different, so you need to look up for whatver you use.
your fbx doesn’t have curves because you probably never animated it.
But if you export an animation from the engine and play it back in the DCC you should see the curves (and other stuff like bones).
You just move things between animations and assuming your mesh was properly set up you are generally good to go. (Obviously it’s an approximation, and not the exact same expression so you do need to tweak some at some point).