Dennis @ PerfectForms
I would create a form with a table with columns for instance ID, a field to identify the instance (Instance Name?), the values you want to insert, and a button.
Create a form connection to the form being edited. Use it to populate the table with the instance IDs and the Instance Names. Type in the data you want changed in the columns of that row. When the button in the table is clicked use a Set Field in Other Instance object using the instance ID in the current row of the table.