Open the Flint Wallet window and click "Send". At the next screen, enable the "Milkomeda mode" toggle, paste the Milkomeda C1 wallet address currently in the clipboard into the "Milkomeda Ethereum Address" field, and enter the amount to send (1 ADA in this example). Then click "Continue".
At the confirmation screen, enter your wallet password and click "Send".
The transfer will require 10 confirmations, which should take approximately 5 minutes. Once the transaction is confirmed, the transferred MilkADA should be visible in your C1 wallet in MetaMask.
Now you have successfully wrapped your ADA into MilkADA for use on the Milkomeda C1 sidechain.