If your address is a simple account; head over to http://wallet.zksync.io/ and withdraw them in browser!
If not, it's a smart contract (like Gnosis Safe):
If your contract can execute arbitrary transactions, you can email Matter Labs or hop in their Discord to ask about the best way to connect it to zkSync (assuming you can't connect to it from https://wallet.zksync.io/).
Alternatively, if you just want to withdraw funds to L1, the easiest way is to use their alternative withdrawal tools. This will let any account force push funds from zkSync to L1 if the address has never interacted with zkSync
Note: If your grant payout address is a Gnosis Safe wallet (smart contract), you will need to create a safe on Polygon where the funds were sent. You can then retroactively claim your contributions. You can do that using these instructions here. If you're having trouble, you can always hop into the Gnosis Safe Discord or Polygon Discord and ask your questions!
How to withdraw from Polygon
Please note that you'll need mainnet ETH to facilitate withdrawal from Polygon network, and the whole process will usually take up to 4 hours to complete. To begin, head on to https://wallet.polygon.technology/bridge/ and connect your MetaMask wallet with same admin address provided during the creation of your grant.
After connecting MetaMask, you should see your Polygon Bridge dashboard set to PoS transfer mode as shown below.
Select PoS-WETH as currency to withdraw from if it isn't the default. Enter the amount you want to withdraw or simply click "MAX" if you desire to withdraw all your ETH from Polygon. After that, click on "Transfer" to proceed.
You would be required to click "Continue" on the three-step pop-up modal that comes up to confirm the transaction fee. Be reminded that the withdrawal process may take up to 4 hours to complete.
After signing the MetaMask notification, the first part of the withdrawal process will take approximately 45 mins to 1 hour. This step will move your L2 funds to a checkpoint on the Ethereum network.
You'll be prompted again to sign another transaction on MetaMask to confirm the transfer of funds from the checkpoint to your MetaMask wallet. This is the second part of the withdrawal process and may take up to 3 hours to complete.
The withdrawal should be complete after 3 hours and you would be able to view your transaction on etherscan.io by clicking "View on Etherscan". Please note that it is safe to refresh your browser.