This cheat needs PPSSPP version 1.13 or up and can be activated by editing the compat.ini file which is in the /assets/compat.ini folder. The location of this folder will depend on the system used, on Windows it will be where PPSSPP is installed, on Android it should be in the /Android/data/org.ppsspp.ppsspp/ folder, etc. With the file open in a text editor, search for [GoWFramerateHack30] and uncomment (remove the #) from the GameID you use (don't uncomment the other lines, just the God of War GameIDs), it should look like this: