From our documentation:
If you have an Oracle 12c database, consider the following:

• Consult your Oracle DB administrator to understand the architectural changes in Oracle 12c.  For more information, refer to Oracle documentation. 
• The following options are available when you choose to use the Oracle 12c database: 
  • If want to use a non multi-tenant database, you must create a non-Container Database (CDB) database.
  • If you want to use a multi-tenant database, you must create a CDB with Pluggable Database (PDB) inside it.

• If you are using non-CDB, no specific settings are required.
• If you are using the CDB with Pluggable Database (PDB) inside it, perform the following steps before installing BMC Remedy AR System:
  1. Create the PDB. For example you could create a database called REMPDB. For more information, see Oracle documentation for Multitenant architecture.

  2. Register the PDB as service to the listener. For more information, see Oracle documentation for Multitenant architecture. 

     Note: During installation choose Oracle service name option in the AR System Server User and Database Information panel.