Clicking on "this link" (e.g., like in the window above) will try to establish a connection with your HUD in a browser tab.
If the connection is successful (you must be logged into SL and wearing the HUD), you should see something like this in the browser tab that opened:
Click the "Advanced" button, and then click on the "Proceed to ..." link all at the bottom of the message.
After doing that, you should see some message from the HUD in the tab (it will just show the RLV version, but you don't need to care about that). You can close the tab.
Now you should be able to use your Wardrobe page normally to interact with your HUD.