You can connect Dentacoin Wallet with Dentacoin Staking platform through WalletConnect. See how here:
What if your DCN or ETH are on Ethereum Mainnet?
You can swap both DCN and ETH from Mainnet to Optimism via Dentacoin Wallet - SWAP feature. It is the most cost effective option (3 - 4$).
With regards to ETH on Optimism, you can purchase it directly via Dentacoin Wallet: wallet.dentacoin.com/buy or through an exchange