Let him be assessed and get him all the help u can by all means, but u can also help a lot yourself. I did with my dyslexic son who ended up going to Oxbridge and is now a uni lecturer.
Not all, but many bright dyslexics have very logical minds and therefore have above average difficulties coping with the inconsistencies of English spelling. My son certainly did.
So i helped him by drawing his attention to the regular and irregular (or sensible and stupid) spellings in words, such as 'and, sand, stand, strand' and 'any, many, apron, father', going over the latter sort repeatedly and explaining that they make no sense but just have to be learned anyway.
The silly words which kept giving him trouble (e.g. trouble), i used to write out on little cards for going over again and again, with a mixture of phonics and sight reading.
I think that what helped him most was being made aware that English spelling is so often silly and therefore makes learning to read and write much harder than need be.