Is there a video refocus feature in FCPX?

I Don't think anything can do that.

That really depends on what "a bit soft" means.

This approach at image sharpening is based on an old Photoshop trick. Do not expect miracles and do not try pushing the effect too far because you'll start to introduce "artifacting" (blocking) — but you should be able to achieve some improvement.

You can try duplicating the clip and place the copy over the original. In the Color Board, set the Saturation to 0. In the Video Inspector, set the Compositing Blend Mode to Overlay, and use the Opacity to adjust the "sharpening" (the effect will increase the contrast somewhat, so perhaps around 75-85%).

If you need more "power", add a High Pass filter to the overlay clip. I have a collection of 28 "raw" Motion filters for FCPX here:

http://sight-creations.com/free_stuff/28motionfilters.zip

and you can find a Highpass filter in there. In general, you would want to reduce the Radius and adjust the Amount.

You can further adjust some sharpening (or at least restore some balance in the contrast) by using the Color Board Exposure tool and Darken the darks and lights and boost the midtones on the overlay copy.

I also have an effect: SC Sharpen Tools available here:

http://sight-creations.com/free_stuff/sc_sharpentools.zip
(a kind of tutorial for the effect is here: https://www.youtube.com/watch?v=P8CEb0K_IZo)

which does all of the above (and a little more) in one filter. It's best setting is "at first drop" and I don't recommend straying far from the default parameter settings.

Good luck.