Updating array elements

I'm a newbie in python. Im trying to insert an array into my database and where an array already exists, should be updated. Below is my code snippet.

query = """
    SELECT  array_remove(ARRAY[(SELECT id FROM s_id f WHERE f.s_id=u.s_id AND f.type_id=2),
    (SELECT id FROM s_id f WHERE f.s_id=u.n_id AND f.type_id=1)],NULL)
    FROM table_a u 
"""

cur.execute(query)

#fetch all rows
link_ids = cur.fetchall()

for count,link_id in enumerate(link_ids):
    print(count+1, "...row")
    table_b = str(link_id[0]).replace('[', '{').replace(']','}')


    check_existance_qry = """
    SELECT * from table_b where table_b_arr = '{}'
    """.format(table_b_arr)

    cur.execute(check_existance_qry)

    results = cur.fetchall()

    rows_returned =len(results)

    if rows_returned == 0: #insert
        query_1 = """
            INSERT INTO table_b (table_b_arr) VALUES ('{}')
            
        """.format(table_b_arr)
        cur.execute(query_1)
        conn.commit()
            

    else: #update
        query_2 = """
            UPDATE table_b SET updated_at = now(), table_b_arr = '{0}' WHERE table_b_arr = '{0}'
        """.format(table_b_arr)
        cur.execute(query_2)
        conn.commit()
  
conn.close()
cur.close()

I have an excluded constraint on table table_b to prevent insertion of an array element that already exists. i would like my code to update where if an array element already exist.

say array {123,321} already exists in my table, if a new entry say {123,543} appears then array {123,321} should be updated to {123,543}.

Apparently, when i run my code. it inserts then when an array with a matching element is found, it terminates the process. Thank you