Sometimes a slot machine owner gets lucky and there is an experienced, helpful person nearby that can help. If you have any casinos close there may be some slot machine techs that make extra money doing service work on the side, you can ask around at the casino about that. Your machine is an older one, so some of the younger less-experienced slot techs may not be familiar with it.
In general, owners have to fix the machine themselves or get the help of a handy friend to help get thru it. Usually it gets no worse than replacing assemblies such as circuit boards, cables, etc. I think of it as just being part of owning a slot machine, you have to sometimes fix it. Since they are too large and heavy to ship to someone for repair owners usually get some advice, then order a replacement part and replace it themselves. If it is a circuit board that is suspected bad sometimes it can be sent out to be tested and repaired. If you describe the problem, what the machine is or is not doing, include as many photos as possible of the problem area, then the folks here will have a better chance of giving good advice. A repair is just a process of steps, each one building off the other until it is fixed.
You'll find lots of help here at NLG, but a big part of the repair will likely need to come from you since that's where the machine is. Another option, not one I hope you end up choosing, is to sell the machine as-is to someone and buy another one that is working. For some people in certain situations that becomes the best option for them.
Good Luck, and Welcome to NLG!