Reply to the ones that help readers
Prioritise recent, low-star reviews with a specific problem. A useful reply shows prospective users that someone is listening.
Keep replies short and specific
Thank them, name the problem in a few words and say what you will do. Avoid long defences and copy-paste replies that read like a form.
Move the detail to support
Give a support address or in-app link and ask for the device and version. Do not collect personal details in a public thread.
Tell them when it is fixed
When a bug is fixed, go back and reply. Reviewers often update their rating when they see you followed up.
Do not argue or ask for stars
Never ask a reviewer to change their rating as a trade for help. Fix the issue, say so, and let them decide.
Feed reviews into the backlog
Tag the recurring complaints and count them monthly. The top ones belong in the product plan, not just in replies.