hi @shawn.shen,
I am one user of Katalon and I guess that you want to get the value of global variable by override value during the execution. If you want to override global variable, please help to refer to this link: https://docs.katalon.com/katalon-studio/docs/execution-profile-v54.html#update-global-variables-during-runtime
In addition, you want to override Email with Global Variable value (not default value), I think this post may be useful: How to set date today in email summary? - Katalon Studio / Web Testing - Katalon Community
FYI