Please see the link here.

This would be the setting to set on non-SQL Warehouse Databricks Clusters

spark.databricks.sql.initial.catalog.name

To change for the all of the SQL Warehouses in a workspace you would use:

databricks unity-catalog metastores assign --workspace-id 1234567890123456 \
                                       --metastore-id 12a345b6-7890-1cd2-3456-e789f0a12b34 \
                                       --default-catalog-name my_catalog