To link your venue page to your brewery page, first log into your brewery page. Click Edit Brewery on the right, and then on Locations:
Now click the Add Location button:
On the form that opens, fill out all of the fields (including address), and then click Add Venue. Search for the venue by name in the search box that will appear on the right, and once you've selected it, click the Add Location button at the bottom once again:
When you're done, make sure the venue appears under Brewery Locations on your brewery page: