According to the way you login to Yumon, withdraw methods are different.

If you connect to Yumon with a social login (Facebook, Google, Apple, Twitter)

First step: export your Yumon wallet private key

1. Connect on app.yumon.world
2. Login with the same social login than on the Yumon games
3. Go to Profile > Settings > Wallet
4. Click “Export private key”
5. Copy the private key
6. Use an Ethereum crypto wallet and import the private key to it

Second step: transfer the ETH from L2 to L1

Follow the Immutable tutorial:

How to withdraw your L2 assets into your L1 Wallet | Immutable Help Center

Third step: use a crypto exchange to withdraw the ETH on your bank account

Use a verified and trustful exchange like Binance, Coinbase or Kraken.