You can't without difficulty, you have to convert them to BTC or ETH and send them to Coinbase or other reputable exchange then cash out in fiat, in a window where all three securities wallets at respective exchanges aren't in maintenance, network isn't blocked by cryptokittes, and you've passed all AML/KYC including possibly justifying where incoming has came from. There are a lot of people that will find cashing out to fiat very difficult hence why some are parking in Tethers even though they aware of the dubious nature, and thus tether is trading at greater than a dollar. Personally, I wouldn't want to touch tether even for a few minutes, as sod's law it would be my luck that Securities & Futures Commission of Hong Kong or Hong Kong police decide to act just at that moment I buy tethers (well technically the problem will be once it's on TV and value drops to 0).