1.Unlock your Metamask wallet
2. Select network tab and click Custom RPC
3. Add the following value to config
Network Name: EtherCore
New RPC URL: https://rpc.ethercore.org
ChainID: 466
Symbol: ERE
Block Explorer URL: https://explorer.ethercore.org
And then click Save button

Next time you can switch network between Ethereum mainnet and EtherCore mainnet

Thank you!