I don’t know if KDE provides such a feature.
Speech recognition is something that is not entirely solved yet. Of course, the big companies like Amazon, Google, Microsoft, and Apple have both the data and the computing power to make such software, but they do not publish it for use on FOSS systems.
So far, there are projects trying to tackle the problem. I don’t know how easy it is, but you might be interested:
As far as I know, this is just a FOSS wrapper around cloud services. For me, this would be too much of an invasion on my privacy… Decide for yourself.
Currently under development. I’m not aware of any application that uses this, but if you’re a programmer, you could try to write a little script yourself. They provide an API.
I hope this helps, perhaps others know more?