Please select 'Networks' at the top of the MetaMask extension app to open the network menu.
Open MetaMask
From the network menu, select 'Add network'
Add network
Select 'Add a network manually'
Add a network manually
Type in the information below as shown in the image, and click 'Save'.
Network name: Klaytn Cypress
New RPC URL: https://public-en-cypress.klaytn.net
Chain ID: 8217
Currency symbol: KLAY
Block explorer URL: https://scope.klaytn.com
Type in the information and Save
Now, when you select the 'Networks' menu in the MetaMask extension app, you will be able to choose the 'Klaytn Cypress' network.