Accessibird is designed for collaboration between website owners and accessibility agencies. The exact flow depends on which side of the relationship you're on.
If you are a website owner
Invite an agency by email or by their public agency ID, then grant them access to the specific websites you want them to manage. Once accepted, the agency can view issues, create tasks and work on fixes alongside you, all without ever needing your login credentials.
If you are an agency
Start by creating your agency profile, including your branding. From there you can invite clients or accept incoming invitations. Every connected website appears in your agency dashboard, so you can manage all of your clients' accessibility work from a single place.