Here's a thread that tells you how moving your funds from @maticnetwork back to Ethereum works:

1. About every 35 minutes Matic Network sends a transaction to Ethereum. This transaction stores on Ethereum information about all transactions that have happened on Matic Network in the last 35 minutes. This is called a checkpoint.

2. To remove funds a user calls the "withdraw(uint256 value)" function on the child ERC20 contract on Matic Network. This burns the users ERC20 tokens on Matic Network so they are gone. This function returns a transaction hash that identifies this transaction.

3. Now the user waits about 30 minutes for Matic Network to submit the next checkpoint to Ethereum, which will include his burn/withdraw transaction.

4. The user calls the maticPOSClient.exitERC20(txHash) function (using maticjs library) on Ethereum. txHash is the transaction hash of the transaction from Step 2. The function generates a proof that proves to the bridge contract that the user really did burn his ERC20 tokens.

5. Seeing that the proof is correct the bridge contract transfers the user's funds to the user on Ethereum.

So to withdraw funds from Matic is a 3 step process: 1. burn tokens on Matic Network. 2. Wait 30 minutes. 3. Withdraw from bridge to your account on Ethereum.