the admin attribute of other users is not getting updated

I have an admin attribute in my users model which is not getting updated, using the admin_approve action as specified, though the admin attribute of the admin is getting updated. Any suggestion or help will be appreciated.

the user controller file contains this:

def admin_approve
@users = User.paginate(page: params[:page])
end

def update_admin
  @user = User.find(params[:id])
  @user.update_attribute :admin, true
  redirect_to (root_url)
end

the route file has this code:

get '/admin_approve', to: 'users#admin_approve'
patch '/admin_approve', to: 'users#update_admin'

the admin_approve view file:

<% @users.each do |user| %>
  <%= form_for(user) do |f| %>
    <%= render user %>
    <%= f.label :admin, class: 'checkbox' do %>
    <%= f.check_box :admin %>
      Make Admin
    <% end %>
    <%= f.submit "Confirm", class: "btn btn-primary" %>
  <% end %>
<% end %>

I have added a migration to users:

class AddAdminToUsers < ActiveRecord::Migration[5.2]
  def change
    add_column :users, :admin, :boolean, default: false
  end
end