You can invite anyone to become a member of your organization (whether they are already member in another organization) using their username or email address for GitHub.com.
In the top right corner of GitHub.com, click your profile photo, then click Your organizations.
Click the name of your organization
After that click on People
Next, Click on Invite member
Type the username, full name, or email address of the person you want to invite and click Invite.
Go to the repository and click on settings
Next click on Collaborators and teams.
Provide access to edit the code based on the user request.
