Which ZenFone you are using ?
Always check Announcements Section to see any recruitments are going on. To be Dr.Zen involve in activities and fill the form like User. Link.
Moderators will recruit you if you performed well.
Good
As of now no beta Tester program is going on for ZF max mobile.
So you have to wait for it. About Dr.Zen to become one fill the form correctly. And check your status every month.