Assuming you have a modded Switch (Atmosphere) or an emulator, here is the standard workflow for applying Update 1.3 to either an XCI or NSP base.
An XCI is a 1:1 copy of a physical game cartridge. It includes the base game (typically 16GB for Engage) plus any data stored on the cart. Fire Emblem Engage Switch XCI NSP Update 1.3....
For the modding community, keeping your copy of Fire Emblem Engage updated to 1.3 ensures compatibility with save editors, texture packs (like the GBA-style battle animations), and future fan-translation fixes. As of late 2024, no further updates are expected, making the final, complete, and definitive way to play the game. Assuming you have a modded Switch (Atmosphere) or