https://support.wix.com/en/corvid-by-wix/wix-stores-with-corvid
https://www.wix.com/corvid/reference/wix-data.WixDataQuery.html
For starters why are you changing your dropdown value toString, especially when you are expecting the contains query to search for the value of it too.
Also your let line should be before you call any function, the data query should really be wrapped up in your function.
Plus, you can’t call a function simply by using function search… You would also be better off using dropdown onChange
https://www.wix.com/corvid/reference/$w.Dropdown.html#onChange
Have a read of these too,
https://support.wix.com/en/article/corvid-working-with-the-properties-panel
https://support.wix.com/en/article/corvid-reacting-to-user-actions-using-events