Microsoft Teams Public Preview activate for "early access"
Public preview for Microsoft Teams provides early access to unreleased features of Microsoft Teams. This preview/examples allows you to explore and test future features. Public preview can be enabled for one individual user, so you don't have to worry about it affecting the entire organization or tenant.
Browse to the Teams administrator panel
Browse to https://admin.teams.microsoft.com/ or through the URL collection page.
Adjust the update policy
Adjust Update Policies in Microsoft Teams.
Select your profile to display the Teams menu.
Select About → developer preview / developer preview.
Select Switch to for developer preview / developers preview
Is the policy not yet visible?
Unfortunately there is only one thing to do, wait. Often at the beginning you will see some of these 3 possibilities. You can always find more information on Microsoft's website.
Place users in first-release
Taking your tenant for one user, multiple users or everyone to a first-release mode is also possible. You can activate these options in this blog.
Put your teams app in Public Preview in Windows 10 or MacOSX
Microsoft Teams Public preview with PowerShell?
Enable Microsoft Teams Public Preview with PowerShell - Matti Paukkonen
Other Microsoft Teams tips and blogs can be found here.