About size drop down box


Good morning,
I want to sell products with size variations, they belong to home and kitchen category
First I created child products then I bundled them under a parent product and I have chosen size as a variation criteria, after adding titles and description, when I click on my product detail page I don’t find the drop-down box that allow a customer to choose between the different sizes or colours that I have, How can I get this drop-down box on my product detail page, please
Kind regards,