After reading the README file for Java Alternator Loadbalancer repository, it mentions the AlternatorDynamoDbAsyncClient which exists in the repository, but in the latest version 1.0.4 of the library it does not exist.
Looks like another release will fix this issue
scylladb/YCSB#29
This is the link for the PR in YCSB to implement the alternator-loadbalancer feature, if I’m doing something wrong in it, please then update the documentation so that It will be clear for customers as well using thing library