Correct me if I'm wrong. What I understand from your question is how to add other credit card to Maybank2u and use it to pay bills.

It's very easy. Just go to account and banking, bill payment, and manage non-maybank credit cards. After that you would be able to use it to pay bills. Bear in mind that not all bills are payable using non-Maybank cards.

If you meant, how to pay other credit card bills using Maybank2u, it's also very easy. Make an interbank transfer to your 16 digit cc account.