What's the best way to clean mobo slots?

[Stoly]

So, I have a couple of supposedly working mobos, it's been a while (year +) since they've been tested.

AMD Gigabyte B550 DS3H/Ryzen7 5700X3d (the CPU is brand new)
Intel GA-H119M-H / Intel Core I7

Thing is both mobos won't boot and show memory beeps.
I know for sure all 4 DDR4 stick work as I've used them in another mobo, so I'm inclined to think the memory slots might need cleaning.

I have isopropyl alcohol and WD40, which should I use?

 

[Grimlakin]

Hit it with air first. Thrn clean it with alcohol and a microfiber no lint cloth. Let dry. Hit with air again.

 

[Denpepe]

I have isopropyl alcohol and WD40, which should I use?

BW-100: Electronic Contact Cleaner

BW-100 Electronic Contact Cleaner Non-Flammable Aerosol Spray - Safely Cleans Joycons, Keyboards, Computers, Rechargeable Devices, and More - Removes Dust, Dirt, and Other Debris

www.amazon.com