In your relationship graph there should be a Table Occurrence (TO) for each table that you have set up from the External Data Source. You can create a layout based on any of those TOs. Place fields from the ESS table on your layout. Then you should be able to edit the data in the fields from your iOS device when you are on that layout.
ESS is supported on an iOS device - obviously only on a hosted file, but I think you have that covered.
The "execute sql" script step however requires a DSN and an ODBC driver to function and those do not exist on iOS. The only way you can use that step and its brother "import from ODBC source" is to use Perform Script on Server.
However as Chris said: since you are using ESS you could just all normal FM script steps because you can treat that data as if it was native to FM.
Thank you so much for the help..
I was making it way more complicated than it actually was.
Now I am able to update values to tables and trying to insert values to related table.
Thanks for all the help:)