How to pass id in form_for from select/4

Given a select menu with a list of user IDs, how can the ID be passed to the show action?

<%= form_for @conn, user_path(@conn, :show, :user_id), [method: :get], fn f -> %>
<%= select f, :user_id, @users %>
<%= submit "Search" %>
<% end %>

The intent is to redirect to, for example, /users/1, where 1 == :user_id

I assume you wanna send the selected one when the user changes the select menu, if that so simple javascript function should do it

Correct. Does that mean form_for is not needed?