Based on https://github.com/Uniswap/uniswap-interface
yarnyarn startTo have the interface default to a different network when a wallet is not connected:
- Make a copy of 
.envnamed.env.local - Change 
REACT_APP_NETWORK_IDto"{YOUR_NETWORK_ID}" - Change 
REACT_APP_NETWORK_URLto e.g."https://{YOUR_NETWORK_ID}.infura.io/v3/{YOUR_INFURA_KEY}" 
Note that the interface only works on testnets where both Uniswap V2 and multicall are deployed. The interface will not work on other networks.