Hi Miccey
Well, like the others mentioned above I also recommend pressurized air (mild alcoholic solvents/pads only in case the pressurized air doesn´t help but keep far away from “flooding” those holes)
Even more -for the future- I recommend pluggable dust covers like the ones in the link below; available from several suppliers. They are pretty cheap and serve me very good by keeping dirt & water off the phone´s inside:
Best
DonFnord