Access 2013: Perform action when a drop-down list item is selected in a form

Hello. I have a drop down list with some items in a form and I want when one of these items is selected, an action to be performed.

To be more specific, there is a list of dates that a person visited my office. When I select a date, I want a subform to open with the details of this (and only this) visit. If a select another date, I want to see the details of this other date.

How easy is this to be performed?

Any help will be appreciated.
Thanks for looking.