A tyre update to a full form Design Approval (DA) is considered a modification to an existing layout.
To make a tyre update to an existing full form DA, you should:
Choose the layout that requires the tyre update; and
Using the 'MANAGE LAYOUTS' menu, choose 'Modify existing layout'.
Then you can complete the application with the updates and submit.
For a short form DA, use the Variations > Tyre options updated application type.