Partner Hub's Messaging tool allows you to get in touch with your brand partner directly. To access it, click Messaging in the navigation header. From there:

• The panel on the right shows your ongoing conversations. Click a message to open it and use the reply box to type and send a response.
• Click the draft icon to send a new message. You can only contact a brand with which you have an active partnership.

You will get a notification each time you receive a new message. Click the bell icon in the navigation header to open the notifications panel.