Invite and manage the users of your Landlord Portal from the Add-ons and Integrations area of the Settings Menu.

Select Landlord Portal, and then Manage Landlord Portal Users.

Use the Invite Owner button to send an email with a link the owner can use to finish setting up their login.

The New Owner Account option lets you select an owner contact and set the password.  Their email address will copy from their contact, if they didn't have one you can add it now.