Delete that file. Rename it back to .z64 . ISO is the wrong format.
The quest to convert Z64 to ISO is a dead end—not because it is difficult, but because it is conceptually impossible. Cartridges and discs are different worlds. Instead of searching for a converter, simply download a modern N64 emulator (Project64 or RetroArch with the Mupen64Plus core), drag your .z64 file into the window, and start playing. z64 to iso