Deselect triggers

I'm not sure what you're asking about. 

Do you simply want to make each date show a ring when it's Selected and have the ring disappear when it's deselected? That can be done without triggers. Just insert the "ring" directly into the Selected state of the date.

• Any object with a Normal and a Selected state will change toggle between those states when clicked. See: PRIMER: Take advantage of built-in states | Articulate - Community 

If you only want one date to be Selected at a time (like you can only choose one answer in the Multiple Choice question), put the dates into a button set. See: Storyline 360: Working with Button Sets | Articulate - Community 

If you want something else to happen based on the selections, I suggest you provide more information about what you're trying to accomplish. And it'll be easier for someone to troubleshoot if you upload a .story file. Here are the best practices for doing that: 

• Only include slides that are related to the problem.
• Be sure objects, layers, motion paths, and variables have meaningful names.
• If there is proprietary content, replace or delete it. For example, replace proprietary text with “ipsum lorem” text.