A not working; C done; B= ?? (source)

This is a comment on Session File Store: inaccessible directory "/tmp", posted by regvg at 20.02.2019 09:21

View source for A not working; C done; B= ??

Tnx for suggestions: 
option A: done, but returned "SessionFileStore: inaccessible directory "/_cache/session""
option C: done, all Windows permissions set to "allow" etc
option B: cannot find file to edit, where exactly is it? 

Tnx again, ciao