How to Add an Administrator to a LinkedIn Company Page

You must be a Company Page administrator in order to add other administrators.

Note: You must visit LinkedIn.com from your desktop and go to the Company or Showcase Page to make admin changes.

To add an admin:

1. Move your cursor over Interests at the top of your homepage and select Companies.
2. Type your company name into the Search for Companies box and select your company name from the list.
3. Click the blue Edit button in the upper right.
4. Scroll down the Overview page and find the Company Pages Admins section on the left. This is below the Company Description and Default Language fields.
5. Under Designated Admins, start typing the name of a connection that you want to be an admin. You must be connected to the new admins through LinkedIn before you can add them.  
• Note: The maximum number of admins for a Company Page is 50.
6. Click Publish in the top right of the page.

Steps taken from: https://help.linkedin.com/app/answers/detail/a_id/37594