To assign a Tenant to a Property, go to the Manage Property dropdown and choose the 'Manage Renters' option here:
From there, scroll to the Add Renter section and the Choose User option here:
Click on the Choose User and you will be provided with all Tenants that have been added to your account. You may choose from that list and choose the 'Save Changes' option below. This will add the Tenant to the Property.
You may also check the 'Email new renter with link...' checkbox to send that confirmation email to your Tenant. This will allow them to set up a password to log in.