Check description of this video for the template:
https://www.youtube.com/watch?v=uaGT15JTeHY

The file "cvc_footstep_uniquename_sound.lua" must be renamed, you just have to change "uniquename".

See the image below...
You just need to rename the part in the red rectangle (the one at the top right), do not remove the "CVC_AdditionalFootStepSound_" part otherwise the new footstep sound will not be recognized.
And put your sounds in the green rectangles (the other two rectangles), see that there is the possibility of choosing which sounds for left foot and right foot.


Image [zupimages.net]