Microsoft Teams Public Preview activation for "early access
Public preview for Microsoft Teams provides early access to unreleased features of Microsoft Teams. With this preview you can explore and test future functions. Public preview can be enabled for one individual user, so you don't have to worry that it will affect the whole organisation or tenant.
Browseto the Teams administrator panel
Adjust the update policy
Adjust the Update Policies in Microsoft Teams.
Select your profile to display the Teams menu.
Select About → Developer View / developer preview.
Select Switch to for developer view / developers preview
Is the policy not yet visible?
Place users in first-release
You can also switch tenant to first-release mode for one user, multiple users or everyone. 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?
Other Microsoft Teams tips and blogs can be found here.