If you download a raw .psu file (PS2 Save Utility format), you cannot use it directly. Use myMC (Memory Card Manager) on Windows to inject the .psu into a blank .ps2 card.
There is no native save editor for RE4 on Android, but you can use RE4 Tweaks (Windows utility) to edit a PC save, then transfer it back. Save Data Resident Evil 4 Aether Sx2
To restore: Load the same game → Load State → pick the slot. If you download a raw