Hi @nick ! 
Normally, the element should close automatically if the ‘close on select’ option is activated. However, it’s possible that, depending on your element’s configuration and options, this default behavior might be overridden.
If ‘close on select’ doesn’t work, there’s a technique you can use to force the element to remount. You can find the instructions on this page: How to Reset a Dropdown Element.
In your case, the idea is to trigger this workflow immediately after changing the value of your select.