Handling numerous parallel requests for modifying license count in a nosql db via nodejs based microservice

I have a node based microservice which is responsible for updating the license items in a nosql database, I have deployed 2 replicas of the microservice attached to a load balancer in a kubernetes cluster. The updation of the license count is done via REST request received to the microservice. Considering that we receive numerous requests in parallel, How do we make sure all the requests work in a sequential manner and deliver a response to the API request? (Working with parallel execution is a problem as when more requests are received we need to make sure the initial requests are handled before)