Rebalance the cluster token range

I’ve a test cluster and it’s load is imbalance. We have keyspace with RF=1.

--  Address     Load     Tokens
UN  146.7 GB   256  
UN  2.85 GB    256  
UN  36.45 MB   256

How can i rebalance this cluster token range?

The Load column indicates the size on disk that ScyllaDB uses. It depends on your data model.
Please share more details about it (tables, primary key, etc.).
Basic data modeling is covered in this ScyllaDB University lesson.
Also make sure you understand tokens and data distribution covered in the ScyllaDB Essentials course.