In the Step 4: Summary screen, you are shown the simple products that will be created as a result of you adding these choices.
Check you are happy and click Next to finish.
Then click Save on the product to confirm.
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Note: You will be able to view and edit your new simple products in the product list after you are done. The new hidden simple products are hidden in the app because the ‘Visibility’ setting of the product is set to ‘Not Visible Individually’.