You are able to add pre-approvals by uploading and importing a list of candidates under the Manage Pre-Approvals link in the portal. You can also add individual pre-approvals one at a time by clicking the Add button in the same section.
Detailed, step-by-step instructions can be found in the Direct Billing Pre-Approval Guide provided in your welcome email.
For an interactive tutorial on how to add pre-approvals, visit the Pre-Approval Information section.