At AllTrack, we refer to the owners of songs as Shareholders, which in most cases includes writers, composers, producers and publishers.
To add a co-shareholder to one of your songs:
Log in to your AllTrack account.
From the "Register a Song" page, select "Add a Shareholder" from the dropdown menu in the Shareholder column, which will lead you to the "Add New Common Shareholder" page.
From the "Add New Common Shareholder" page, input the relevant data to search for your co-Shareholder.
If the search identified the proper co-Shareholder by their relevant name and IPI#, select the checkbox of co-Shareholder and select the "Add Shareholder" button at the bottom of the page. If the search did not identify the proper co-Shareholder, select the button that allows you to add them manually.
From the "Register a Song" page, select the newly added co-Shareholder from the dropdown menu in the Shareholder column.
You can log in to your AllTrack account here.