welcome to the forum. There really isnt a way to clean it properly but having run into the same problem I did have some temporary success with washing
a filter in petrol. I'd only recommend trying this on the primary filter ( 1st one after tank ) which I assume that is.
Got us another 10 hrs motoring but we were back in the marina after that so don't know how long its good for.
It was on a 6.5 hp diesel so only minimal fuel flow as well but a lot smaller filter too.
Worth a try if he's desperate.