Etherscan has both mainnet and testnet explorers for users to access to and these explorers can be accessed from any Etherscan Ethereum explorers under a single dropdown. Through this, users can access Ropsten, Kovan, Rinkeby and Goerli Testnet explorers along with BeaconScan (Eth2) and Ethereum Mainnet in Chinese. Now, let's move to how to use this feature.
In the navigation bar (which can be accessed from any page on Etherscan), there is a square button with the Ethereum logo located at the end of the navigation bar. Once users hover on the logo, there will be a dropdown that lists the aforementioned contents. From there, users can access the testnet by clicking on the provided links. Mind that, the link will open a new tab on your browser.
Similarly, users can access the Ethereum Mainnet explorer from the testnet explorer by following similar steps.
In the testnet navigation bar, there will be a button at the end of it and unlike the mainnet, it will show the name of the testnet instead of the Ethereum logo. Another thing to note is that opening the mainnet explorer page from the testnet will not open a new tab. It will open on the same page instead.
Lastly, changing to BeaconScan Testnet requires similar steps but once users on the page itself, they are not able to access the Ethereum Testnets from Beacon Testnet other than Goerli Testnet.