It does not matter that the date tag was input on another screen. The TinyDB
shares the tags across screens. What you place in the Tag you want to clear is a DATE.
In your ListPicker, the event contains both the date and the event. Separate the date from the event information using the red Text blocks. You can use the following blocks:

The TinyDB block is shown from the other screen ONLY to show where the Tag date comes from.
Change your blocks and try your app. It should properly delete the event you select..
Regards,
Steve