How to scale horizontally a microservice that contains a database

Imagine a microservice of & # 39; User & # 39; which contains all the logic related to the user, and this microservice has a database.

How could you scale this microservice horizontally and maintain consistency?

In fact, if you single add another instance, then, if a user is created, updated or deleted, the operation would only be applied in one instance and, as a result, would lose coherence.

What is the most convenient way to scale horizontally and maintain consistency?