Basically... you want to do:

1. File -> New\Restore (Pick a name)
2. Select - "Wallet with Two Factor Authentication" (option 2)
3. Select - "I already have a seed"
4. Enter your seed (it should say "Seed Type: 2fa", next to "Options" button)
5. Select - "Keep"
6. After clicking "Next" a couple of times, enter the email you originally used
7. Either put in your GAuth Code... or tick the "I have lost my Google Authenticator Account" box and keep going.

Once you've completed, you should be able to use: "Wallet -> Master Public Keys" and you should see CoSigner 1, 2 and 3