Sysaux tablespace purging

Find the biggest occupants:
select * from v$sysaux_occupants where space_usage_kbytes>1048576 order by 6;
Or the segments:
col owner for a20
col segment_name for a30
select owner, segment_type, segment_name, bytes/1048576 from dba_segments where tablespace_name='SYSAUX' and bytes>104857600 order by 4;

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If the top occupants are 'SM/OPTSTAT' and 'SM/ADVISOR', you could follow
How To Purge Optimizer Statistics Advisor Old Records From 12.2 Onwards (Doc ID 2660128.1)
probably changing v_min_age from 30 to 20 or 10 days:

set serveroutput on
DECLARE
    v_oldest INTEGER := 730;    -- Two years
    v_increment INTEGER := 50;
    v_cur_age INTEGER;
    v_min_age INTEGER := 20;     -- Retain one month. Change to 20 days
BEGIN
    v_cur_age := v_oldest;
    WHILE v_cur_age >= v_min_age LOOP
        dbms_sqltune.set_tuning_task_parameter(task_name => 'AUTO_STATS_ADVISOR_TASK', parameter => 'EXECUTION_DAYS_TO_EXPIRE', value => v_cur_age);
        prvt_advisor.delete_expired_tasks;
        v_cur_age := v_cur_age - v_increment;
    END LOOP;
EXCEPTION
    WHEN OTHERS THEN
        dbms_output.put_line('Execution halted with error number ' || sqlerrm);
END;
/

followed by moving table WRI$_ADV_OBJECTS and rebuilding its unusable indexes. The advantage of this code in the document is better than
exec prvt_advisor.delete_expired_tasks
because the latter will almost always throw ORA-1555 ("snapshot too old").

However, even the small step cleanup using the above PL/SQL code is not ideal; it will generates lots of redo and archive log and it runs many hours. The best and cleanest solution is a simple truncate. Follow Step 3 of
SYSAUX Tablespace Grows Rapidly After Upgrading Database to 12.2.0.1 or Above Due To Statistics Advisor (Doc ID 2305512.1) to simply truncate table WRI$_ADV_OBJECTS.[note]

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If the top occupant is heatmap, follow
HEATMAP Segment Size Is Large In SYSAUX Even When Heatmap=Off (Doc ID 2024036.1)

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If it's unified auditing records, follow
How To Purge The UNIFIED AUDIT TRAIL (Doc ID 1582627.1)

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[note] Ref:
SR 3-33612933171
in spite of
Can I Truncate Objects in SYSAUX if they are Taking up too much Space? (Doc ID 1928156.1)