Please follow the below steps to install Built-In/URP version:

1, Copy Built-In.unitypackage or URP.unitypackage to some where outside your project, 

2, Remove everything in 'Assets/SoftKitty/MasterCharacterCreator' folder except the following folders from your Built-In/URP project:
"ArtSource"
"Documentation"
"Scripts"  
"Textures"

3, Import the Built-In.unitypackage or URP.unitypackage you just copied.