When a group is created, there is an option to set up the group administrator with access to the content or with administrative capabilities and no access.
If you are a no-access group administrator and would like content access, you can change your account type in your My Account dashboard as long as you have an empty seat available in your group.
Click My Account in the upper right corner of the site and then click View Account. Click the "Group Members" tab and navigate to your name on the list. Change the dropdown for Account Type to Standard Subscription (or KLplus option, if applicable).
If you do not have an empty seat available, you will need to purchase one through the Upgrade button.