Hi Goncalo,
New Tenant means a different User Management. For example you only have one application for 2 or more completely different companies (Tenants).
We have the default Tenant (Users) but to add new users to a tenant that you create you should create a new user. That user will be saved in User table but with a different TenantId for you will be able to manage the Users per Tenant.
Imagine a big company that have 2 brands, one stronger other low cost, they have a multi tenant application to manage purchases. You (a person) are client from the 2 brands, you are a person but you will have 2 users. For me doesn't makes sence switching users from tenants and because of that you don't see that action here and I don't know you requirements but sounds me strange.
You have great information related from Multi-Tenant provided from Outsystems and because the Outsystems built-in User application is not able to manages Users in a Multi Tenant environment this application is realy good to you understand how should work and adapt it to your needs.
Kind regards,
Nuno Oliveira