This is the easiest way to add a 100% save without messing with your file directories.
The file is formatted specifically for the .ps2 memory card structure used by AetherSX2. How to Install the Fixed Save Data on AetherSX2
Navigate to your device's storage: Android > data > xyz.aethersx2.android > files > memcards .
Locate your downloaded .ps2 or .max save file and select it.