Show order total on the Edit page as the details table is updated

with this article I was able to populate totals from detail to master.
guide: https://xlinesoft.com/phprunner/docs/show_order_total_on_the_edit_page_as_the_details_table_is_updated.htm

But the Text Box looses its property in the master. I want the value to appear in my existing TextBox of a master field so that it can be saved.

the code that needs to be modified is in the custom_functions.js section:
// update totals if the 'totals' element is inserted into the master page
pageObj.findItem('total').text( parseFloat(value).toFixed(2) );

can anyone help me please to replace above code so that the result appears in my existing textbox that can be saved?

with regards