Oracle Enterprise Manager Database Express, also referred to as EM Express, is a web-based tool for managing Oracle Database 12c. Built inside the database server, it offers support for basic administrative tasks such as storage and user management, and provides comprehensive solutions for performance diagnostics and tuning.

task#6 Use Enterprise Manager Database Express 12c ( EM12c) and alter the state of the pluggable database PDBORCL from open to close, and again from close to open.
step#1 – Connect to EM 12c. Open the browser with “localhost:5500/em” and enter SYS username/password.

The Enterprise Manager Start Page

Then open the window that shows pluggable databases PDBs state.

The List of Oracle 12c Pluggable Databases

The pluggable database PDBORCL is open in Read Write mode, it has been running for 6 hours and 31 minutes, and its size is 2GB.
step#2 – Open the List of possible Actions on pluggable databases.

The Action List

The pluggable database PDBORCL could be:
-Cloned
-Plugged or Unplugged
-Dropped
-Closed

step#3 – Click on the Close option to close the pluggable database PDBORCL

The Pluggable Database is Closed

The pluggable database pdborcl is now closed.
step#4 – Open the pluggable database pdborcl in Read Write mode.

The Pluggable Database

step#5 – Open SQL window and see the SQL statements that will be executed to open the pluggable database pdborcl in Read Write mode.

SQL statements that will be executed

step#6 – See the confirmation message that the pluggable database pdborcl is successfully opened.

The Pluggable Database is OPEN

Summary
The Enterprise Manager Database Express 12c allows the DBAs and Oracle Developers clean, fast, and effortless control over the root CDB and pluggable PDBs.

Reference

Oracle 12c documentation

EM12c