You could use sodium hypochlorite or household bleach at as low a strength, as will kill the mould. Having said that a lot of household bleach has a lot of sodium hydroxide or caustic soda in it these days, which you definitely don't want as it will only rot the fabric.

Hydrogen peroxide at a low concentration may be safer and do the same job.

Either of these solutions will turn a black top white. I'd give it a quick scrub and leave the rest to sunlight.

That'll be a canvas top.

Clean it, paint it with renovator to bring back the colour and then treat it with waterproofer. Once it cannot get wet, it will not go mouldy. You efforts will also be rewarded in that it'll look a lot nicer too.

Anyone who's ever owned a car with a duck canvas top knows you have to do this every couple of years, unless you like having a roof that looks like a mouldy pair of faded jeans.