PPSSPP is a standalone emulator, not a retroarch core. So they do not relate at all.
You can restore ppsspp(and many other) settings to their muOS defaults by going to applications>task toolkit>restore tasks.
There’s a task there to restore ppsspp to defaults.
Opening the app via the applications tab and adjusting over there should also work, but there is a bug in the current release that prevent that from working.
You can read more about that, and install an update to fix it, looking here: PPSSPP Configs not adopted when starting directly into game (Trimui Brick) - #2 by bgelmini