my project -> property -> SQL -> OpenESQL -> <ADD> -> Select <DBMAN> -> After that, I can't select ODBC, so I can't use ODBC.
Although it appears that you can't select ODBC (in the Add Directive dialog), go ahead and click OK to add the directive. It will add the DBMAN directive with its default value of ADO. Once it's been added (and the Add Directive dialog has closed), you should be able to change its value to ODBC. In other words, it takes two separate steps: first, add the directive with its default value, and then change the value.
Also, in order to use the OpenESQL Assistant with ODBC, you may need to change the mode from ADO to ODBC. Go to Tools -> Options -> Micro Focus -> OpenESQL Assistant, and in the right pane under General, change the mode from ADO.NET to ODBC.
I hope this gets you one step closer!