If the project has already been uploaded to Architizer.com by another firm:
Add your firm as a collaborator by clicking +Add Collaborating Firm on the Project Page
If you are uploading the project:
Click the grey link labeled +Add Collaborating Firm on the bottom left side of the Project Page
Type the firm name and select their profile from the dropdown menu.
If the firm doesn’t have an Architizer profile, email us at firstname.lastname@example.org