Steps to reproduce:
1. Log in as a subscriber on target WordPress site. 
2. View the page source of /wp-admin and command+f to search for "proxySetupURL"
3. Copy the URL that should look something like: https:\/\/\/site-management\/setup\/? 
4. Open the previously copied URL in a new tab.  
5. Sign in with any Google account and just follow the prompts - the site will be added to your search console at the end.