Organization owners can unblock a user who's previously been blocked, restoring their access to the organization's repositories.
When you unblock a user from your organization, they'll be able to contribute to your organization's repositories.
In the top right corner of GitHub, click your profile photo, then click Your profile.
On the left side of your profile page, under "Organizations", click the icon for your organization.
Under your organization name, click Settings.
In the Settings sidebar, click Block users.
Under "Blocked users", next to the user you'd like to unblock, click Unblock.
Tip: Settings that were removed when you blocked the user from your organization, such as collaborator status, stars, and watches, are not restored when you unblock the user.