After getting the BIOS I'd recommend putting it in the same folder as your emulator.

How to use it VBA - RR: Options - Emulation - Select BIOS file - Use BIOS file

Bizhawk: Place the BIOS file in the Firmware folder where Bizhawk is located. e.g.

You'll know you have it if this is ticked in: Config - Firmwares

mGBA: Tools - Settings - BIOS - GBA BIOS.