1) Go to the settings page
2) Click on Networks > Add Network
3) Key in the relevant details:
RPC URL: https://http-testnet.hecochain.com
Block Explorer: https://testnet.bscscan.com
RPC URL: https://http-mainnet.hecochain.com
Block Explorer: https://scan.hecochain.com
For more information on how to use MetaMask with Huobi ECO Chain (HECO), you can check it out here.