Duplicates split everything you've earned, reviews, ranking history, citations, and confuse both Google and customers. First move: inventory them (search Maps for your name, address variants, and phone).
The fix depends on access: if you can claim the duplicate, do so, then report it for removal/merge as a duplicate of your primary (Business Profile help center handles merges. Reviews can often be merged into the surviving profile on request). If it's unverified junk data, 'Suggest an edit' → flag as duplicate works from the outside.
Choose the SURVIVOR deliberately: keep the profile with the review history, kill the stray. And fix the source (old addresses in directories breed duplicates; the citation cleanup prevents recurrence).