OpenSea is compatible with several blockchains. To switch chains, click on the blockchain icon within your wallet sidebar and select the chain you’d like to switch to.
Depending on your wallet provider, you may see a confirmation screen in your wallet extension. Here’s an example from MetaMask:
If you’ve logged in with a third-party crypto wallet, such as MetaMask, you can also switch blockchains within your wallet extension, which will automatically switch the chain on OpenSea: