Contributors can be given additional permissions to edit the Site Template (e.g. appearance of the published knowledge base). Follow the steps below to add that permission to a contributor.
In the screenshot below, you can see the site that the user has access to (Luna has access to the Academy Site). If this is the correct site, click the Limited Access option under Admin Area Access.
If you do not see the site in this view, it means that the site has not yet been added to the user's profile. Follow these instructions to add a site to a user's profile: Creating Contributor Permission Rules for a User.
If it says, Full Access in the Admin Area Access column, then the user already has permission to edit the site template.