If your institution already has a dashboard in Peergrade you will be asked to join if you signed up with the institutions email.

If you use a personal email instead of using your institution's email you can still join the institution. The admin in charge of your Peergrade institution will need to invite you using the email you used to sign up for Peergrade. Once you've been invited you can accept the invitation sent to you trough email or simply go to Peergrade and accept the invitation on your user overview.