Help with Atomstack A5

I have just changed my laser machine for a Atomstack A5. Can anyone help with settings regards the Home button not working or the machine not auto homing on startup. I have read that the $21= 1 is what is needed, but I can’t get it to change from $21=0. Machine will go home if I press go to origin, and all other settings that I have tested seem to work ok. Nice machine which could be better if it went home using the Home button. Please help if you can.