where should I write my helper's method with domain route?

I am using a domain route Admin

class Admin::MembersController < ApplicationController

so I have my views in app > views > admin > members
and my helpers in app > helpers > admin > members (module
Admin::MembersHelper)

fine, it's running well

in one of my application layouts partials , _members.html.erb, I try to
use a method
<%= filtrate(current_user) %>

but I get an error
ActionView::TemplateError (undefined method `filtrate' for
#<ActionView::Base:0x32ea330>) on line #7 of layouts/_members.html.erb:

I wrote the filtrate method in my Admin::MembersHelper ... is it wrong ?
why ?
where should I write it ?

thanks for your help

I wrote the filtrate method in my Admin::MembersHelper ... is it wrong ?
why ?
where should I write it ?

thanks for your help

found the problem.... I was trying to use the wrong helper,I should
have look after the current controller at this time...