Oracle 12: Using compound trigger to update data in same table on each insert/update
There is no need for a compound trigger. Use simply
CREATE OR REPLACE TRIGGER customer_info_trg
    BEFORE UPDATE OR INSERT ON custommer_info
    FOR EACH ROW    
BEGIN
    :NEW.last_upd_by := USER;
    :NEW.last_upd_time := SYSTIMESTAMP;
END;