I found a Galaxy machine and documented the instruction and menu navigation for others!
Galaxy Arachnid Bullshooter Electronic Dartboard instructions for free play mode (these instructions are for Galaxy v 7.02):
1. While holding the button on the main board with cabinet open - turn on the machine.
2. This will boot the machine into Setup Menu.
3. Using select and enter buttons select option 2. Machine Setup Menu
4. Using select and enter buttons select option 6. Coinslot Assignment Menu
5. Using select and enter buttons select the last option - Free Play Option - set to ON