From the Coinbase mobile app:
Read moreCan I transfer ETH to USDT on Coinbase?
Use your ETH to buy Compound USDT in the trade tab Then tap on the “Trade” tab, where you can swap ETH for any token that runs on the Ethereum standard (called “ERC-20 tokens”). Tap “choose coin” and select Compound USDT. Input the amount of ETH you’d like to exchange for Compound USDT.
Read more