How to retire a physical standby in Oracle 11.2
The unique names of the databases in a Data Guard configuration are listed in the log_archive_config parameter in the following form:

log_archive_config='DG_CONFIG=(PDB10,PDB10_STBY)'


You can remove the old one and add the new one as:

alter system set log_archive_config='DG_CONFIG=(PDB10,PDB10SBY)';


After this, you can set log_archive_dest_N to the new standby.