To set up the MetaMask for the Polygon, you should add a custom RPC. To accomplish this, first, click on the Network Selection button at the top of the MetaMask app.
Next, click on Custom RPC. You will find the Custom RPC option at the bottom. The next step will be to add the expected data as shown below:
Polygon (Matic Network) to Metamask
Network name: Matic Mainnet
New RPC URL: https://rpc-mainnet.maticvigil.com/
Chain ID: 137
Currency symbol: MATIC
Block Explorer URL: https://explorer.matic.network/
Once you have added the URL in the New Network field, click on Save. You will now see Matic’s Mainnet in the network dropdown list of your metamask, and can simply switch between Ethereum and Matic networks.