How to set the current schema in a session

alter session set current_schema=SCOTT;

The CURRENT_SCHEMA parameter changes the current schema of the session to the specified schema.
Subsequent unqualified references to schema objects during the session will resolve to objects in the specified schema.
The setting persists for the duration of the session or until you issue another ALTER SESSION SET CURRENT_SCHEMA statement.

This setting offers a convenient way to perform operations on objects in a schema other than that of the current user
without having to qualify the objects with the schema name.

This setting changes the current schema, but it does not change the session user or the current user,
nor does it give the session user any additional system or object privileges for the session.

Source: Oracle Documentation