How do I uninstall 123 Timer for Teams?

1. From the left of the Teams desktop client, select Apps.
2. On the page that opens, scroll to the bottom and select Manage your apps.
3. Find the app you'd like to remove.
4. Select the arrow to expand and view recent context in Teams where you've used the app. Select Remove for each context from which you'd like to remove the app.

Read here for more instructions on uninstalling apps from Teams.