Dodging and Burning
There are many skin softening programs out there, but none yet that do as good a job and good old 'dodging and burning'
There are some true masters of the art out there and I'm not one of them but an example of what can be achieved even at a basic level is shown below.
On the left you can see the shot straight out of camera. In Affinity Photo (could also be photoshop or other processing programs that allow layers) I put a 50% grey layer on top of the original and set it to 'soft light'. Then it is just a matter of painting black (burning) onto the grey layer where the skin is too light - and white (dodging) where the skin is too dark.
This results in a skin texture that still looks natural, but a lot smoother.
It takes a lot of time and if you are going to try it I suggest using a drawing tablet such as those made by Wacom.