Help needed changing percentage on Vivid Viva Las Vegas Machine

[Matthew73]

I purchased a Vivid Viva Las Vegas Fruit Machine about two years ago. The percentage payout is currently set on 90% and I would really like to lower this. I'm unsure how to do this. I've had a look inside the machine and cannot see a stakes and prizes key anywhere nor can I see a socket where I could insert one. Would anyone be able to advise if it possible to change it on this machine. If I need to get a stakes and prizes key, can anyone advise where it needs to be plugged in? Any help is highly appreciated.