I have followed Tron Foundation for months and I think that if you want to swap USDT-OMNI or USDT-ETH for TRC20 based USDT, it's better to follow the official / latest instruction from Tron Foundation: https://medium.com/@Tronfoundation/how-to-swap-your-usdt-omni-or-usdt-eth-for-trc20-based-usdt-32fa4eb87437