You can link your Apple ID with Touch n' Go by searching "Apple Zone" in Touch n' Go,
You can also enter Apple Zone by clicking 【More】at the Touch n' Go home page and find 【Tickets & Entertainment】and click on the Apple icon. Then you can link Apple Services by clicking 【Link Now】.
If you have any other issues during this process, please contact Apple Support:
https://getsupport.apple.com/.