How to cleanup temporary tablespaces in a PDB and create new ones in the right location

Notice how temporary tablespace groups can be used instead of directly referencing the temporary tablespace name:

alter session set container=PDB1;

CREATE TEMPORARY TABLESPACE TEMP3
TEMPFILE
  '/disk1/oradata/PDB1/temp03.dbf' SIZE 20G AUTOEXTEND ON NEXT 128K MAXSIZE 20G
TABLESPACE GROUP TEMP_NEW
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 1M
FLASHBACK ON;

ALTER DATABASE DEFAULT TEMPORARY TABLESPACE TEMP_NEW;

DROP TABLESPACE TEMP1 INCLUDING CONTENTS AND DATAFILES;
DROP TABLESPACE TEMP2 INCLUDING CONTENTS AND DATAFILES;

CREATE TEMPORARY TABLESPACE TEMP1
TEMPFILE
  '/disk1/oradata/PDB1/temp01.dbf' SIZE 1G AUTOEXTEND ON NEXT 128K MAXSIZE 20G
TABLESPACE GROUP TEMP
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 1M
FLASHBACK ON;

CREATE TEMPORARY TABLESPACE TEMP2
TEMPFILE
  '/disk1/oradata/PDB1/temp02.dbf' SIZE 1G AUTOEXTEND ON NEXT 128K MAXSIZE 20G
TABLESPACE GROUP TEMP
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 1M
FLASHBACK ON;

ALTER DATABASE DEFAULT TEMPORARY TABLESPACE TEMP;

DROP TABLESPACE TEMP3 INCLUDING CONTENTS AND DATAFILES;

exit

More about temporary tablespace groups in Oracle 19c here