Hit, "C" key to bring up your character panel.
In the panel you should see a drop-down box above your character's head.
Select your desired build.
Close the character panel.
Hit "Escape" key and bring up your Interface panel.
Select the "AddOns" tab at the top.
Click "TopFit" from the left panel list of addons.
Check both, "Show set values in tooltip" and "Show item comparison values in tooltip".
Then in the "Automatic update set" drop-down box, select your desired build.
Close the Interface panel.
I suggest re-logging to save your steps.
I hope this was helpful enough.
