In Business Profile Manager:
Click Create group and name it.
Click Add business, then Import businesses.
Upload a spreadsheet of all locations (you can download Google’s template).
Click Select file to upload.
Fill in every relevant field: store code, name, address, locality and sub-locality, latitude and longitude, phone numbers, website (the location page, not the homepage), categories, hours and special hours, opening date, photos, attributes, amenities, payment methods, and menu or booking URLs.

Bulk verification. With 10 or more locations of the same business, you can request bulk verification rather than verifying one by one. Eligibility is strict: locations must be physical premises customers can visit (service area businesses aren’t eligible), share the same business name and categories, and match the locations listed on your website. Once bulk verified, new locations can usually be verified much faster.
Avoid common pitfalls:
Don’t let service areas overlap between locations. It’s a suspension risk.
Don’t add keywords or location names to business names unless they’re part of the real-world name. It breaks Google’s guidelines.
Set a clear process for who updates hours, services and photos at each branch, and how quickly.
Keep hours accurate above all. Being open at the time of search is a top-five local pack factor.