From time to time we start working with a client that has existing and often claimed Google+ pages that they don't have access to. In many cases we know that these pages were created by a former SEO who isn't willing to give them access to their Google+ login for one reason or another, or a former employee who has since left the company. When this is the case, these are the steps to take to gain or regain ownership:
1) Go ahead and try to claim.
2) The system will let you know that someone else has verified the listing.
3) Click Request Admin Rights. You’ll be asked to answer some questions about the business.
4) Google will send the current owner an email asking them to get in touch with you.
5) Wait one week. If you don’t hear back in a week, click contact us to talk to phone support and they'll help you.
Official Google Help Docs explain what to do step-by-step here: https://support.google.com/business/answer/4566671?hl=en
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