If you're connecting your own business listing (Google My Business)

3. Click Continue
4. Select your business listing from the dropdown:

5. Click Select to save the listing.
If you're connecting a profile you're not an admin of (Google Place)
1. Enter the Google+ profile ID in the field and click Add.

2. Click Continue.
3. Click Find Place to search for the Google Place.

4. Choose the address from the list and click Select.

5. The Google Place will now show right next to the competitor page:

6. Click Select to save the listing and start monitoring your competitor's business reviews.
IMPORTANT NOTE: If you are an existing user who have Google Places already connected for your own business, all you need to do is to reconnect your Google+ profile and the associated My Business Listing should appear right next to the page.