1 - Open Metamask, and select "Custom RPC" from the Network Dropdown.
2 - In the "Custom RPC" Settings, add in the IDChain network details and click Save:
Network Name: IDChain
New RPC URL: https://idchain.one/rpc/
ChainID (Optional): 74
Block Explorer URL: https://explorer.idchain.one
Note: If IDChain doesn't appear on Metamask, try reinstalling Metamask.