The process will be similar for any 3rd party ERC20 Wallet on chain wallets like MEW, Trezor, etc.
Step 1: Login into your Metamask wallet.
Step 2: Copy the CAS-ERC20 address to Deposit, which you can see in CAS Swap section.
Step 3: Enter the copied address in Metamask
Step 4: You have to confirm again to make a transaction.
Step 5: The Transaction will be confirmed.
Step 6: You can see your CAS token on CAS Swap section