Rails how to download only current record when clicked download button

I'm new to rails. Im developing an app which contains adding customers.In that I have download button.When I click download button It should download the current customer page in csv file.

Controller

def create
  @customer_detail = CustomerDetail.new(customer_detail_params)
  @customer_detail.company_profile_id = current_user.company_profile.id
  respond_to do |format|
    if @customer_detail.save
       format.html { redirect_to edit_customer_detail_path(@customer_detail), notice: 'customerDetails was successfully created.' }
      # format.html { render 'edit', notice: 'customerDetails was successfully created.' }
    else
      format.html { render :new }
    end
  end
end

def index
  @customer_details = CustomerDetail.all
end

def destroy
end

def update
  respond_to do |format|
    format.html
    format.csv { render text: @customer_details.to_csv }
    if @customer_detail.update(customer_detail_params)
      format.html { redirect_to @customer_detail, notice: 'customer_details was successfully updated.' }
    else
      format.html { render :edit }
    end
  end
end

View

.fieldset
  .row
    .col-sm-3
      = f.submit "Save", class: "btn btn-primary"
    .col-sm-3
      = f.submit "cancel", type: :reset, class: "btn btn-primary"
    .col-sm-3
      = link_to "Download", edit_customer_detail(format: "csv"), class: "btn btn-primary"
    .col-sm-3
      = link_to("Print", "javascript:print()", class: "btn btn-primary")

The problem is it downloads all the records from of the form. I dont know whether to action is to be given in update or edit.If i give the path edit_customer_detail instead of customer_details_(path) it shows template error and no route matches error when clicking download button.can someone please help me.I've attached the output link here. thanks in advance!!

Customer_details.csv