You should receive an email when we receive a payment that needs help with remittance, as described in this article. If you lose track of that email, the page is easily accessible from within the app.
Find the "Payment" navigation item on the left side of our app. If there are any unapplied payments, there will be a red badge next to this showing the number of unapplied payments that we've received. See below for an example.
From the "Payments" page, notice that payments with unapplied amounts are not greyed out and are actionable. Click one of these to get to the "Payment" page. From there click the "Apply" tab to get to the page where you can provide remittance. See this article for more information on how this page works.