Option 1 One way is to alter the current session and do transaction.
alter session set current_schema=SYN_BI;
But show user will still show sys if u connect as sys
Option 2 – Create user and give connect access
create user temp_bi identified by temp_bi;
grant connect ,resource to temp_bi;
alter user SYN_BI grant connect through temp_bi;
SQL> conn temp_bi[SYN_BI]/temp_bi
Connected.
SQL> sho user
USER is “SYN_BI”