First, do all of this with the power off. You don’t want to accidentally short some sort of coil voltage into the switch matrix. That’ll give you way more problems.
To clean the contact, take a business card, dip the corner in some rubbing alcohol, then slide that part between the contacts. Use a finger to gently hold those contacts together, then slide the business card out. Repeat a few times.
Then test the switch. You may not need to adjust anything.
Still not working?
Inspect how the contacts act as a ball rolls over the switch. If they’re obviously making contact, don’t mess with it. If not, needle nose pliers are OK if you don’t have one of these
https://www.pinballlife.com/ultimate-leaf-adjuster-tool.html
Gently bend the switch so that they’re normally open, but making good contact when the ball rolls over the switch.
Also, inspect the wiring to the switch. Give each wire a gentle tug to make sure it’s still connected well.
That’s how I’d start.
Remember, power off.
Jeff