1) Download the reset database tool: https://ftp.reallusion.com/reallusionsupport/ResetDBForIC8CC4.zip
2) Close iClone 8/Character Creator 4 program.
3) Uncompress the "ResetDBForIC8CC4" to local drive.
4) Double click the related .bat file to run it.
5) Wait around 30 seconds for rebuilding the database.
6) Done.