If you are considering downloading it from an unofficial source, I strongly advise against it unless you can verify its origin and contents in an isolated environment (e.g., a virtual machine with no network access).

In this long-form article, we will break down exactly what Gxrom.bin is, why your emulator is asking for it, where it originates from, and the safest methods to acquire it without infecting your computer with malware.

For more specific help, search for your alongside "firmware download" to find the correct software to rename.