begin
  for part in (
    select partition_name from user_tab_partitions 
    where table_name = '<your table>'
      and <your other conditions>
  )
  loop
    execute immediate 'alter table <your table> truncate partition '||part.partition_name;
    dbms_output.put_line ('Partition '||part.partition_name||' truncated');
  end loop;
end;
/

SQL> DROP TABLE TBL PURGE
  2  /

Table dropped.

SQL> CREATE TABLE TBL(
  2                   BRAND VARCHAR2(10),
  3                   YEAR  NUMBER
  4                  )
  5    PARTITION BY LIST(BRAND,YEAR)
  6    (
  7     PARTITION BRAND1_2022 VALUES(('BRAND1',2022)),
  8     PARTITION BRAND2_2022 VALUES(('BRAND2',2022)),
  9     PARTITION BRAND1_2023 VALUES(('BRAND1',2023)),
 10     PARTITION BRAND2_2023 VALUES(('BRAND2',2023))
 11    )
 12  /

Table created.

SQL> INSERT INTO TBL VALUES('BRAND1',2022)
  2  /

1 row created.

SQL> INSERT INTO TBL VALUES('BRAND2',2022)
  2  /

1 row created.

SQL> INSERT INTO TBL VALUES('BRAND1',2023)
  2  /

1 row created.

SQL> INSERT INTO TBL VALUES('BRAND2',2023)
  2  /

1 row created.

SQL> COMMIT
  2  /

Commit complete.

SQL> SELECT * FROM TBL PARTITION FOR('BRAND1',2023)
  2  /

BRAND            YEAR
---------- ----------
BRAND1           2023

SQL> EXEC EXECUTE IMMEDIATE 'ALTER TABLE TBL TRUNCATE PARTITION FOR(''BRAND1'',' || TO_NUMBER(TO_CHAR(ADD_MONTHS(SYSDATE,-5),'YYYY')) || ')'

PL/SQL procedure successfully completed.

SQL> SELECT * FROM TBL PARTITION FOR('BRAND1',2023)
  2  /

no rows selected

SQL>