You can only add one column in the SELECT DYNAMIC - OPTIONS NAME : confer_radio_talent_institute
The OPTIONS VALUE should also be confer_radio_talent_institute
And your STORAGE FIELD should be the same
You can of course create a separate dropdown for each field/column in your database.
The alternative that you are looking for to have 4 columns/fields together may require you to create a separate dropdown with dates (seb_datefield) and then use that search field with an advanced SQL query using the SEARCH QUERY product www.seblod.com/products/19157
something based on this :
SELECT fieldname, fieldname2, fieldname3 FROM #__yourtablename WHERE [MATCH]firstcolname|| $uri->getValue('seb_datefield')[/MATCH]
OR [MATCH]2ndcolname|| $uri->getValue('seb_datefield')[/MATCH]
OR ...
If there is a simpler way perhaps someone else can point it out...but I am sure you can do it with the solution I proposed above.