Hello @Axendia-Monica ,
Your personal LinkedIn account that you're logging into will need to be either the owner or an appointed admin of the LinkedIn company page you wish to connect.
LinkedIn support's article on adding admins to company pages
As far as adding a signup form to your LI company page or other LI profiles, we'd recommend using the landing page sign up form since social pages tend not to allow 3rd party scripting to be added, just links.
See also:
Syncing social pages with your Constant Contact account
Setting up LinkedIn company pages
Creating landing page sign up forms
... View more
