Open the site's contact list
Adding a beneficiary works exactly like adding a contact; the steps below say "contact" and note the beneficiary label where it differs. You need a role with Create & edit permission for the list (see Who can see and edit contacts and beneficiaries).
Open the site (for example from the project dashboard's site list, or Sites in the top bar).
Select the CONTACTS tab (or BENEFICIARIES). The tab shows how many records the site has, a Search box, Filters, a download button and the green ⊕ CREATE button.
Select CREATE. Two choices appear:
Create contact - fill in a new person from scratch.
Create contact from existing user - pick one of the project's Zite users and start from their details (the Fetch Contact Details dialog lists them; search by name).