Search your business name on Google Maps, hit 'Own this business?' (or start at google.com/business), sign in with the Google account you want owning it — a business account you control, not an employee's personal login — and verify by the method offered (postcard, phone, video, or email varies).
Then complete everything: exact categories, hours, service area, photos, services. Completeness is a ranking input, and half-filled profiles quietly lose to finished ones.
If someone else already claimed it (an old marketer, a previous owner), Google has a request-ownership flow that emails the current holder and escalates after a waiting period. Start it immediately — that profile holds your reviews.