Hi Lames.
Thank you.
In table dba_unused_col_tabs (select * from dba_unused_col_tabs;) I saw a lot of tables, I check them and found needed table. After I run
alter table mytab drop unused columns;
It don't help I sow error ORA-12996. Finally I made online reorganization this table use DBMS_REDEFINITION.
Best regards.
Alexander Ignatenko