When user Unsubscribed,What do I do to subscribe again?

Hi!

I'm glad to your nice support.Thanks.
Then,I have a question.

I use your e-Newsletter plugin and Membership plugin together.

In my test case,When I get a mail from plugin,and click "Unsubscribe Instantly.",Surely Unsubscribed.

Then,Next,I tested subscribe again by admin user like follows.

https://premium.wpmudev.org/forums/topic/a-user-on-my-multisite-accidentally-unsubscribed-to-one-email-by-my-mass-email-sender-feature-and-wants-back-on-how-do-i-do-this

But I can't find out
'Users > All Users, click the Edit link for the user. Scroll down to the bottom and set "Receive admin emails"'

If Administrator subscribe user again,What do I do?

P.S.
I watch my db table called wp_enewsletter_members and find a column which Unsubscribe user's row's 'unsubscribe_code' is empty.
Is this related?