You can no longer add yourself as a manager of profiles managed by your collaborators. Unfortunately, this feature was being abused by some users, so we have made the decision to remove it.
If you would like to be added as a manager of a profile managed by a collaborator, then you may send a management request. See our FAQ: How can I request management of a profile?
Or you may choose to follow the profile to receive public updates about the profile in your newsfeed. Simply click the "Follow" button at the top right of the profile page.