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Field return value Help in the order page

Hello everyone and thanks for your attention
I’m building a small ecommerce site for a coffee shop that provides booking, online payment, and pickup for the next day at the point of sale.
I’m not very familiar with html and css, and on the checkout page I saw that you can’t add form blocks.
I should insert a field where there is a dropdown menu where to select the time, and this I did.
Then, however, in the “order” page, which is the one that the cafeteria receives via e-mail for confirmation, I should insert a field that receives the value entered in the dropdown menu of the checkout field and thus know the withdrawal time.
How can I do?
Thank you

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