Before downloading any ROM, you need an emulator that can read .gba files. These are the best options for Android:
To play the Pokémon Indigo League GBA ROM on your Android device, you'll need a compatible emulator. Here are some popular options: Pokemon Indigo League Gba Rom Download For Android
Download the .ips or .bps patch file and a clean Pokémon FireRed (U) (V1.1) ROM. Use an online patcher (like RomPatcher.js) or mobile app (Unipatcher) to apply the patch. Before downloading any ROM, you need an emulator