Based on Google's official help: how to reply to reviews on a Business Profile, how a reply gets published, how to edit or delete it, and how to report inappropriate reviews.
Steps for replying
According to Google's official help, you must complete owner verification for the business before you can reply to a review.
The steps are to open the Business Profile and choose the option to read reviews, select the reply icon next to a review, type your response in the box that appears, and send it.
Before a reply is published
Replies are checked against Google's content policy. If a reply is not approved, you are asked to edit it. The help page says the check usually takes about 10 minutes, but can occasionally take up to 30 days.
An approved reply appears below the review and is shown as coming from the business, not from an individual. The reviewer is notified, and may read the reply and update their review, in which case a new date is displayed.
Editing, deleting, and problem reviews
You can edit a reply from the reviews screen using the edit icon under your reply. To remove it, select the delete icon and confirm, then save the change with the update button.
If you think a review violates policy, you can report (flag) it. The official help points to a separate guide for the detailed steps. It also notes that reviews are available only in some countries and for some business types, and that availability can change.
This article is based on the official documentation, and the specifications may change.
TAKEAWAY
What this means for your project
Check that owner verification is complete on your Business Profile. Then go through unanswered reviews, newest first, and add short, polite replies, such as a thank-you or a request to check the facts. Google's help says courteous replies show that you are responsive. If a review seems to break the policy, use the reporting process instead of replying.