Click on your profile picture in the upper right and then click on "Add another account"
for the sign in email address, enter in either yournetid@wisc.edu and click "Next"
You should be prompted with a normal NetID authentication window which you can again enter your NetID and password followed by a Duo Mobile login.
After that, you should be signed into your @wisc.edu Google account and have access to the various things that are accessible to you there.
Should you later need to toggle back and forth between your Google identities, you can click on your profile picture and click the alternate identity. (See the picture above.)