To swap BTC for USDT in DeFi, use platforms like Uniswap, PancakeSwap, or 1inch. Connect your wallet (e.g., MetaMask) and select the BTC and USDT trading pair. Since BTC is a native asset, you might need to use a wrapped version (WBTC) for DeFi swaps. Enter the amount, review the exchange rate and fees, and confirm the transaction. Ensure you're using a reputable platform to avoid potential risks. Always double-check the transaction details and be aware of market volatility and potential slippage. The process is relatively straightforward and can be completed in a few steps.