Fund your MetaMask wallet on Avalanche with USDC.e or AVAX. For USDC.e, you can do this by bridging USDC from your MetaMask wallet on Ethereum using https://bridge.avax.network/login . You can purchase the AVAX token on a centralized exchange (Coinbase, KuCoin, etc.) that permits Avalanche “C-chain” withdrawals.
Once you have AVAX or USDC.e in your MetaMask wallet on the Avalanche network, you can swap it for OH on Trader Joe. Be sure to leave some AVAX in to pay the transaction fees.