Sell your Stellar's for bitcoin at Binance as a start and then exchange your bitcoin for fiat.
You can't withdraw to fiat from Blockchain so you'll have to use an exchange platform. Depend on where you are from, I suggest the following ones: Coinbase, Bitstamp, Bitpanda, Coinmama, Kraken.
Or he could use website like shapeshift, changelly or blocktrade for the conversion rather than going through regular crypto exchange.
These sites offer direct conversion and do not require registration in most cases.