A requirement to convert a 12c database to CDB with a single pluggable database (PDB). Please help t

A requirement to convert a 12c database to CDB with a single pluggable database (PDB). Please help to identify the supported method.

Currently while checking the database upgraded is having following status.

SQL> select

decode(sys_context('USERENV', 'CON_NAME'),'CDB$ROOT',sys_context('USERENV', 'DB_NAME'),sys_context('USERENV', 'CON_NAME')) DB_NAME, decode(sys_context('USERENV','CON_ID'),1,'CDB','PDB') TYPE from DUAL;  2

DB_NAME

--------------------------------------------------------------------------------

TYP

---

ATGISG

PDB

Please suggest to identify the supported method with reference Notes