Drupal 7 dropdown list on Ubercart form

Hi, I need a mandatory select drop-down list to be added to an Ubercart product page(s) that shares the user selection with the Ubercart customer email order confirmation, probably in the form of a token.

Relative to the URL shown below, there is already a single Entity Reference field (Sir John McDougal Gardens, E14), however, I want this to become a drop-down list that selects from multiple notes. For example, each person trainer has their own profile (node) and I want the users to be able to select a personal trainer based on their location, and the user needs to make this selection before they can submit the order.

Interestingly, I can already select the personal trainers by location in the form but this functionality is not rendered (exposed) in the web page (see attached).

https://justenoughexercise.com/ease-yourself-option

Please let me know if you have any questions. Thank you