When you are in Pancake Swap, navigate to the trade screen

Click “Connect” at the top right of the screen, and then navigate to “Trade” on the left sidebar.

If using Metamask, go to Settings –> Networks –> Add Network
And put in this information…

Network Name: Smart Chain
New RPC URL: https://bsc-dataseed.binance.org/
Chain ID: 56
Symbol: BNB
Block Explorer URL: https://bscscan.com
Network Name: Smart Chain