Before you start, make sure that you have added Optimism Network to your wallet. Check the user guide for instructions. Once completed, you will see your DCN tokens on Optimism in your wallet.
1) Note that swapping tokens from one network to the other initiates a transaction on the blockchain. And, as all other token transactions, it is processed by miners against a transaction fee in the blockchain-native token ETH. Make sure you have enough ETH in your wallet to complete the swap.
2) Go to: https://gateway.optimism.io/ and Connect your wallet. For MetaMask, choose "MetaMask", for TrustWallet, choose "Wallet Connect".
3) Confirm the connection of your wallet to Optimism Gateway:
For TrustWallet, go to Settings in your wallet app and choose "WalletConnect" to scan the QR code.
For MetaMask, confirm the connecting of the walle to gateway.optimism.io in your wallet.
4) Once your wallet is connected, search for Dentacoin or DCN from the list of tokens. You will see the current balance. Enter the amount you would like to swap to DCN on Ethereum Mainnet and click "WITHDRAW".