Per another comment in this thread, that is only accessible to "verified Tether customers", which means you payed them directly for the USDT. If you bought it off Coinbase for some ETH, you don't have any right to recoup it from them (though presumably Coinbase or whoever sold it to them does).
Also, they reserve the right to delay fulfilling your order indefinitely, so they don't actually guarantee anything even if you did buy directly from them.
You can transfer it from exchange to your own Wallet and then sell it back to Tether. Though you need at least $100K worth of USDT and you need to pay transfer fee to the exchange. It's bit of a hassle (and costs money) but can be done.
Also, they reserve the right to delay fulfilling your order indefinitely, so they don't actually guarantee anything even if you did buy directly from them.