Update 2 tables with one form

Rails
1

I have a form:

<% form_tag :action => ‘create’ do %>
<%= hidden_field_tag ‘plan’, params[:plan] %>

<% fields_for :account do |f| %> 
<%= f.text_field :name %>

  <%= f.text_field :domain %>.<%= AppConfig['base_domain'] %>
<% end %>
<% fields_for :user do |f| %> <%= f.text_field :login %>
<%= f.text_field :eservice %> PPL Eservice Login (If Known)
<%= f.text_field :first_name %>
<%= f.text_field :last_name %>
<%= f.text_field :email %>
<%= f.text_field :contact_number %>
Password <%= f.password_field :password %>
Password Confirmation <%= f.password_field :password_confirmation %> <% end %>

I would like to only have the second part of the form and have the
fields first_name last_name update the account table name and have
login update the account table domain. Do you know how to do this?

Thank you,

Sean McGilvray