If you're looking to move tokens from the Ethereum network, or any other EVM-compatible network, back to BSC, then you're in luck:
Binance has written a support article specifically to help you out with this. Its suggests it's specifically about recovering funds sent on the wrong network, but it also covers some important general points about moving funds to BNB Smart Chain.
Keep in mind that MetaMask simply allows you to access the Binance network, and has nothing to do with how tokens work, or get transferred onto or off BSC. For this reason, we encourage you to consult directly with Binance's support resources for all Binance-related issues.
Make sure to ask Binance for any special requirements before making a transaction.
If you have any further questions regarding Binance, please contact the Binance Support team directly.