At the present time you can only set up one site on the mobile app.
To add other sites to the same email address please log into https://my.howz.com with your app credentials, select 'Sites', and then 'Create site'. You will then be taken through the set up process to add a new site. Simply select your default site to show your preferred site on the app. We are working to bring multi-site viewing to the app as soon as possible.