How do I remove a country once its selected, using the "select country" widget?

I am trying to create a donation form that will allow parents to select a country along with their donation. I found the "select country" widget, but I need to now how to remove the country, once its chosen.

I am not exactly sure what you are trying to achieve. Do you want to remove county from the map on Select Country, so that same country can not be selected by another user? 

Unfortunately that is not possible to achieve. 

If you want prevent that same country is selected more than once, you can use Appointment Slots widget or Ticket Purchases widget and all list of all country's as possible options and set all available options to 1. This way once some country is selected, it will be unavailable for other users.

Hope this will help. Let us know if you need further assistance.